Display Device

ABSTRACT

A cooling device is provided, where an LED backlight can be efficiently cooled in order to suppress display unevenness caused by heat generated from the LED backlight. In addition, a display device including the cooling device is also provided. A display device is provided, where the LED backlight can be cooled by arranging a coolant pipe on a back surface side of the LED backlight and supplying a coolant to a coolant pipe. Further, a display device is provided, where cooling efficiency of the LED backlight can be more improved by arranging a thermal conductor between the LED backlight and the cooling device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a configuration of a backlight which isarranged in a liquid crystal display. In particular, the inventionrelates to a backlight which is formed of a light-emitting diode and aconfiguration of a cooling device which is arranged for the backlight.In addition, the invention relates to a configuration of a displaydevice including a backlight which is formed of a light-emitting diodeand a configuration of a cooling device which is arranged for thebacklight.

2. Description of the Related Art

A liquid crystal display is expected to have a larger screen, and bereduced in weight, thickness, and power consumption compared to aconventional cathode-ray tube (CRT). In recent years, a liquid crystaldisplay has been used for various display devices such as TV and amonitor for a personal computer.

Since liquid crystal elements do not emit light by themselves, forexample, a backlight which functions as a light source is arranged on aback surface portion of a liquid crystal panel. Conventionally, althougha cold cathode fluorescent tube in which hydrargyrum or xenon is sealedin a fluorescent tube (Cold Cathode Fluorescent Lamp: CCFL) is employedas the backlight, there is a problem in that a color reproduction areais small.

Therefore, in recent years, a technique where three colors oflight-emitting diodes (Light Emitting Diode: hereinafter described asLED in this specification), which are red, green, and blue are employedas backlight as a substitute for a cold cathode fluorescent tube hasbeen attracted attention. By employing an LED to a backlight, a colorreproduction area is remarkably wider than a conventional cold cathodefluorescent tube and further a color which is difficult to realize in adisplay utilizing a fluorescent material such as CRT or plasma displaycan be expressed. In addition, since a driver circuit of the backlightcan be simplified compared to a conventional display device, cost can bereduced.

Meanwhile, when a liquid crystal display having a backlight isconsecutively used, the large amount of heat is released. Sincecharacteristics of liquid crystal elements or elements such as atransistor which drives the display device change by this heat from thebacklight, this becomes a possible cause for a display defect such ascolor unevenness or a malfunction. In addition, the heat from thebacklight becomes a possible cause for deformation of the displaydevice. More particularly, in the case of employing an LED to thebacklight, display unevenness or color unevenness is generated sincecharacteristics of LED itself change by heat from the LED.

Thus, in order to radiate the heat from the backlight, various means forradiation of heat are provided. For example, as a conventionaltechnique, an air-cooled cooling device where the heat is radiated bysending cooling air to the backlight with a cooling fan is employed (seeReference 1: Japanese Published Patent Application No. 10-96898).

However, in an air-cooled cooling device, since oscillation is generatedby an operation of a cooling fan and noise is generated by hissing soundof a cooling fan, it requires new countermeasures for oscillation andnoise. In addition, since the amount of heat generation increases as aliquid crystal panel is enlarged, there is concern in that the heatcannot be cooled enough only by an air-cooled cooling device.

SUMMARY OF THE INVENTION

In view of the foregoing problems, it is an object of the invention toprovide a cooling device which can efficiently radiate heat generatedfrom an LED backlight and has a cooling capability, an LED backlighthaving the cooling device, and a display device including the LEDbacklight and the cooling device.

A display device in accordance with one aspect of the invention includesa liquid crystal panel, a backlight, and a cooling device for coolingthe backlight. The backlight includes a plurality of LEDs. The coolingdevice includes a pipe and a coolant flowing through the pipe. Thebacklight and the cooling device are in contact with each other, and thebacklight and the cooling device are arranged on one side of the liquidcrystal panel.

Note that in a display device of the invention, a backlight may bearranged between a liquid crystal panel and a cooling device.

Note that in a display device of the invention, the cooling device maybe arranged between the liquid crystal panel and the backlight.

Note that in a display device of the invention, a backlight is arrangedbetween a liquid crystal panel and a cooling device and the backlightand the cooling device may hold a thermal conductor therebetween.

A display device in accordance with one aspect of the invention includesa liquid crystal panel, a backlight, and a cooling device for coolingthe backlight. The backlight is arranged on one side of the liquidcrystal panel, and the backlight includes a plurality of LEDs which arearranged on one side of a backboard. The cooling device includes a pipeand a coolant flowing through the pipe. The pipe is arranged on theother side of the backboard.

A display device in accordance with one aspect of the invention includesa liquid crystal panel, a backlight, and a cooling device for coolingthe backlight. The backlight is arranged on one side of the liquidcrystal panel, and the backlight includes a plurality of LEDs which arearranged on one side of a backboard. The cooling device includes a pipeand a coolant flowing through the pipe. The pipe is arranged on theother side of the backboard and is not in contact with the LED at thesame time.

A display device in accordance with one aspect of the invention includesa liquid crystal panel, a backlight, and a cooling device for coolingthe backlight. The backlight is arranged on one side of the liquidcrystal panel, and the backlight includes a plurality of LEDs which arearranged on one side of a backboard. The cooling device includes a pipeand a coolant flowing through the pipe. The pipe is arranged on one sideand the other side of the backboard. The pipe which is arranged on oneside of the backboard is not in contact with the LED.

A display device in accordance with one aspect of the invention includesa liquid crystal panel, a backlight, a cooling device for cooling thebacklight, and a thermal conductor. The backlight is arranged on oneside of the liquid crystal panel, and the backlight includes a pluralityof LEDs which are arranged on one side of a backboard. The coolingdevice includes a pipe and a coolant flowing through the pipe. Thethermal conductor is held between the other side of the backboard andthe pipe.

A display device in accordance with one aspect of the invention includesa liquid crystal panel, a backlight, a cooling device for cooling thebacklight, and a thermal conductor. The backlight is arranged on oneside of the liquid crystal panel, and the backlight includes a pluralityof LEDs which are arranged on one side of a backboard. The coolingdevice includes a pipe and a coolant flowing through the pipe. The pipeis arranged on one side of the backboard and is not in contact with theLED. The thermal conductor is arranged on the other side of thebackboard.

A display device in accordance with one aspect of the invention includesa liquid crystal panel, a backlight, a cooling device for cooling thebacklight, and a thermal conductor. The backlight is arranged on oneside of the liquid crystal panel, and the backlight includes a pluralityof LEDs which are arranged on one side of a backboard. The coolingdevice includes a pipe and a coolant flowing through the pipe. A part ofthe pipe is arranged on one side of the backboard and is not in contactwith the LED. The thermal conductor is held between the other surface ofthe backboard and the other part of the pipe.

Note that in a display device of the invention, a thermal conductor isformed from a material having conductivity and may be electricallyconnected to a terminal of an LED.

Note that in a display device of the invention, a pipe and a thermalconductor are formed from materials having conductivity. The pipe isconnected to the thermal conductor. A terminal of an LED may beelectrically connected to at least one of the pipe and the thermalconductor.

Note that in a display device of the invention, at least one of LEDs maybe superposed to a pipe with a backboard interposed therebetween.

Note that in a display device of the invention, a backlight may includea reflecting means for reflecting light emitted from an LED. Thereflecting means may have unevenness.

Note that in a display device of the invention, one side of a liquidcrystal panel is a back surface side of a display surface of the liquidcrystal panel.

Note that in a display device of the invention, a diameter of a pipe isgreater than or equal to 1/100 and less than or equal to 1/10 of ashorter one of vertical length and horizontal length of a backlight.

Note that in a display device of the invention, a backlight is dividedinto a plurality of cooling regions and a pipe may be arranged in eachof the cooling regions.

A lighting device in accordance with one aspect of the inventionincludes a backlight illuminating light to a liquid crystal panel, and acooling device for cooling the backlight. The backlight includes aplurality of LEDs. The cooling device includes a pipe and a coolantflowing through the pipe. The backlight and the cooling device are incontact with each other.

Note that in a lighting device of the invention, a backlight and acooling device may hold a thermal conductor therebetween.

Note that in a lighting device of the invention, a pipe is formed of amaterial having conductivity and the pipe may be electrically connectedto a terminal of an LED.

Note that in a lighting device of the invention, a thermal conductor isformed from a material having conductivity and the thermal conductor maybe electrically connected to a terminal of an LED.

A cooling device in accordance with one aspect of the invention cools abacklight illuminating light to a liquid crystal panel. The coolingdevice includes a pipe and a coolant flowing through the pipe. Thebacklight and the cooling device are in contact with each other.

Note that in the invention, the description “connection” has the samemeaning as the description “electrical connection”. Accordingly, inconfigurations disclosed in the invention, another element which enablesan electrical connection (e.g., another element or a switch) may besandwiched between elements having a predetermined connecting relation.

Note that in the invention, a type of a transistor which can be appliedis not limited to a certain type. A thin film transistor (TFT) using anon-single crystalline semiconductor film typified by amorphous siliconor polycrystalline silicon, a transistor formed by using a semiconductorsubstrate or an SOI substrate, a MOS transistor, a junction transistor,a bipolar transistor, a transistor using a compound semiconductor suchas ZnO or a-InGaZnO, a transistor using an organic semiconductor or acarbon nanotube, or other transistors can be applied. In addition, atype of a substrate over which a transistor is arranged is not limitedto a certain type. The transistor can be arranged over a singlecrystalline substrate, an SOI substrate, a glass substrate, a plasticsubstrate, or the like.

Note that various types of transistors may be employed in the invention,and such transistors can be formed over various types of substrates.Accordingly, all of the circuits may be formed over a glass substrate, aplastic substrate, a single crystalline substrate, an SOI substrate, orany other substrates. Alternatively, some of the circuits may be formedover a substrate while the other parts of the circuits may be formedover another substrate. That is, not all of the circuits are required tobe formed over the same substrate. For example, a part of the circuitsmay be formed with transistors over a glass substrate while the otherparts of the circuits may be formed over a single crystalline substrate,so that the IC chip is connected to the glass substrate by COG (Chip OnGlass). Alternatively, the IC chip may be connected to the glasssubstrate by TAB (Tape Automated Bonding) or a printed wiring board.

Note that a transistor in the invention may have a top gate structure ora bottom gate structure.

In this specification, a semiconductor device means a device having acircuit including semiconductor elements (e.g., transistors or diodes).The semiconductor device may also include all devices that can functionby utilizing semiconductor characteristics. A display device includesnot only a display panel itself where a plurality of pixels includingdisplay elements such as liquid crystal elements or EL elements areformed over the same substrate as a peripheral driver circuit fordriving the pixels, but also a display panel attached with a flexibleprinted circuit (FPC) or a printed wiring board (PWB).

Note that in this specification, when it is described that pixels arearranged in matrix, the description includes not only a case where thepixels are arranged combining a vertical stripe and a lateral stripe,that is, in grid, but also a case where dots of three color elements(e.g., RGB) are arranged in so-called delta pattern in the case ofperforming a full color display with three color elements. Note that thecolor elements are not limited to three colors, and color elements withmore than three colors may be employed; for example, white may be usedin addition to RGB. Further, sizes of light-emitting regions may bedifferent in respective dots of color elements.

Note that in this specification, a lighting device corresponds to adevice having a function of illuminating light. In addition, a coolingdevice corresponds to a device having a function of cooling an object.

Note that following display elements can be applied as appropriate as adisplay element. For example, a display medium, the contrast of whichchanges by an electromagnetic action, such as an EL element (e.g., anorganic EL element, an inorganic EL element, or an EL element containingboth organic and inorganic materials), an electron-emissive element, aliquid crystal element, electronic ink, a grating light valve (GLV), aplasma display (PDP), a digital micromirror device (DMD), apiezoelectric ceramic display, or a carbon nanotube can be applied. Notethat display devices using an EL element include an EL display; displaydevices using an electron-emissive element include a field emissiondisplay (FED), an SED-type flat panel display (SED: Surface-conductionElectron-emitter Display), or the like; display devices using a liquidcrystal element include a liquid crystal display; and display devicesusing electronic ink include electronic paper.

Note that in this specification, a front surface corresponds to asurface which is near the display surface. In addition, a back surfacecorresponds to a surface which is distant from the display surface.

By employing a cooling device of the invention, the heat generated fromthe LED backlight is radiated very efficiently and the LED backlight canbe cooled quickly; thereby, a display defect such as display unevennessor color unevenness caused by the heat generated from the LED backlightcan be prevented. Further, by utilizing the thermal conductor which isarranged between the LED backlight and the cooling device as anelectrode for applying a voltage to the LED, the heat generated from theLED backlight itself can be decreased and further power consumption canbe reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a diagram showing, a configuration of a display device of theinvention;

FIG. 2 is a view showing a configuration of an LED backlight of theinvention;

FIGS. 3A and 3B are views showing a configuration of an LED backlight ofthe invention;

FIG. 4 is a view showing a configuration of an LED backlight of theinvention;

FIGS. 5A and 5B are diagrams showing a configuration of an LED backlightof the invention;

FIGS. 6A and 6B are diagrams showing a configuration of an LED backlightof the invention;

FIG. 7 is a view showing a configuration of a cooling device of theinvention;

FIGS. 8A and 8B are views showing a configuration of a cooling device ofthe invention;

FIGS. 9A and 9B are diagrams showing a configuration of a cooling deviceof the invention;

FIG. 10 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 11 is a diagram showing a configuration of a cooling device of theinvention;

FIGS. 12A and 12B are diagrams showing a configuration of a coolingdevice of the invention;

FIG. 13 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 14 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 15 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 16 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 17 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 18 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 19 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 20 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 21 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 22 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 23 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 24 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 25 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 26 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 27 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 28 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 29 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 30 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 31 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 32 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 33 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 34 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 35 is a diagram showing a configuration of a cooling device of theinvention;

FIGS. 36A and 36B are diagrams showing a configuration of a coolingdevice of the invention;

FIGS. 37A and 37B are diagrams showing a configuration of a coolingdevice of the invention;

FIGS. 38A and 38B are diagrams showing a configuration of a coolingdevice of the invention;

FIG. 39 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 40 is a diagram showing a configuration of a cooling device of theinvention;

FIG. 41 is a diagram showing a configuration of a cooling device of theinvention;

FIGS. 42A and 42B are diagrams showing a configuration of an LEDbacklight of the invention;

FIGS. 43A and 43B are diagrams showing a configuration of an LEDbacklight of the invention;

FIGS. 44A and 44B are diagrams showing a configuration of an LEDbacklight of the invention;

FIG. 45 is a diagram showing a configuration of a cooling device of theinvention;

FIGS. 46A and 46B are diagrams showing a configuration of a coolingdevice of the invention;

FIG. 47 is a diagram showing a configuration of a cooling device of theinvention;

FIGS. 48A and 48B are diagrams, showing a configuration of a coolingdevice of the invention;

FIGS. 49A and 49B are diagrams showing a configuration of a coolingdevice of the invention;

FIGS. 50A and 50B are diagrams showing a configuration of a coolingdevice of the invention;

FIGS. 51A and 51B are diagrams showing a configuration of a coolingdevice of the invention;

FIGS. 52A and 52B are diagrams showing a configurational example of adisplay device of the invention;

FIG. 53 is a diagram showing a configurational example of a displaydevice of the invention;

FIG. 54 is a diagram showing a configurational example of a displaydevice of the invention;

FIG. 55 is a diagram showing a configurational example of a displaydevice of the invention;

FIGS. 56A to 56C are diagrams showing a configurational example of adisplay device of the invention;

FIG. 57 is a diagram showing a configurational example of a displaydevice of the invention;

FIG. 58 is a diagram showing a configurational example of a displaydevice of the invention;

FIG. 59 is a diagram showing a configurational example of a displaydevice of the invention;

FIG. 60 is a block diagram showing a configurational example of adisplay device of the invention;

FIGS. 61A to 61D are views showing examples of electronic devices towhich a display device of the invention can be applied;

FIG. 62 is a diagram showing a configurational example of a displaydevice of the invention; and

FIGS. 63A and 63B are diagrams showing a configuration of a coolingdevice of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the invention will be described by embodiment modes withreference to the drawings. However, the invention can be implemented byvarious modes and it is to be understood that various changes andmodifications will be apparent to those skilled in the art. Unless suchchanges and modifications depart from the scope of the invention, theyshould be construed as being included therein. Therefore, the inventionis not limited to the following description.

Note that in the diagrams of this specification, the same portions orportions having the same function are denoted by the same referencenumerals and repetitive description is omitted.

Embodiment Mode 1

First, a configuration of a display device in this embodiment mode isdescribed with reference to FIG. 1.

FIG. 1 shows a configurational example of the display device in thisembodiment mode. The display device in this embodiment mode includes aliquid crystal panel 101, an LED backlight 102, a cooling device 103, orthe like. The LED backlight 102 is arranged on a back surface side ofthe liquid crystal panel 101 and the cooling device 103 is arranged on aback surface side of the LED backlight 102. Note that the cooling device103 is arranged so as to be in contact with the LED backlight 102. Inaddition, a liquid cooling type cooling device is employed as thecooling device 103 in the invention.

Note that in this specification, the liquid crystal panel 101 is amaterial which needs a backlight, for example, a transmissive type or asemi-transmissive type. In addition, MVA (Multi-domain VerticalAlignment) method, PVA (Patterned Vertical Alignment) method, IPS(In-Plane Switching) method, FFS (Fringe Field Switching) method, andthe like are given as specific examples of a driving method. Note thatspecific examples of the liquid crystal panel 101 are not limited to theaforementioned examples.

Note that in this specification, pixels are arranged in active matrix inthe liquid crystal panel 101. In addition, the liquid crystal panel 101includes a substrate arranged with a transistor. Note that a peripheralcircuit may be formed over the same substrate as the substrate overwhich the transistor is arranged. Further, the transistor which isarranged in the liquid crystal panel 101 may be a transistor formed ofamorphous silicon or a transistor formed using polysilicon.

Next, a configuration of the LED backlight 102 in this embodiment modeis described with reference to FIG. 2, FIGS. 3A and 3B.

FIG. 2 shows a plan view of the LED backlight 102 in this embodimentmode when it is seen from a front surface side of the LED backlight 102.The LED backlight 102 in this embodiment mode includes an LED 201, awiring board 202, a backboard 203, a screw 204, or the like.

Note that a board in which the LED is arranged is referred to abackboard. Thus, the backboard is provided in a back of a light-emittingdirection of the LED.

The LED backlight of this embodiment mode includes an LED array 205where a plurality of LEDs are arranged from side to side (on an X-axisside in FIG. 2) in one wiring board 202. The LED array 205 is attachedto the backboard 203 by using the screw 204. In a configurationalexample of the LED backlight shown in FIG. 2, three LED arrays (205 a to205 c) are provided and arranged up and down (on a Y-axis side in FIG.2). Each of the LED arrays 205 a to 205 c is attached to the backboard203 by using the screw 204.

Note that although the LED are arranged in grid in FIG. 2, the inventionis not limited to this. The LED may be arranged in delta pattern.

In addition, FIG. 3A shows a plan view of the LED backlight 102 shown inFIG. 2 when it is seen from the X-axis side in FIG. 2. Further, FIG. 3Bshows a plan view of the LED backlight 102 shown in FIG. 2 when it isseen from the the Y-axis side in FIG. 2.

Note that the LED 201 is arranged over the wiring board 202 byconnecting terminals 206 a and 206 b of the LED 201 to the wiring board202 as shown in FIG. 3A.

Note that the LED 201 which is arranged over the wiring board 202 may bea white LED, or may be arranged with three colors of LED of R (red), G(green), and B (blue) alternately. Alternatively, the LED 201 which arearranged over the wiring board 202 may be arranged with four colors ofLED of R, B, and W (white) alternately. Alternatively, the LED 201 whichare arranged over the wiring board 202 may be arranged with six colorsof LED of R, G, B, Y (yellow), C (cyan), and M (magenta) alternately.Further alternatively, the LED 201 which is arranged over the wiringboard 202 may be arranged with six colors of LED of two kinds of red(R1, R2) each having a different wavelength, two kinds of green (G1, G2)each having a different wavelength, and two kinds of blue (B1, B2) eachhaving a different wavelength alternately.

Note that in the LED arrays 205 a to 205 c, the LED 201 are preferablyarranged from side to side (in the X-axis side in FIG. 2) and intervalsbetween LED which are adjacent to each other are to be narrow when theLED 201 is arranged over the wiring board 202. This helps light of threecolors of R, and B easily mix with each other particularly in the caseof arranging the three colors of LED of R, G, and B alternately;thereby, uniform white light can enter the liquid crystal panel 101.Accordingly, color unevenness can be reduced.

Note that the intervals between LED which are adjacent to each other arepreferably to be wide when the LED arrays 205 a to 205 c are attached tothe backboard 203. This helps the heat generated from the LED 201 beradiated efficiently so that a temperature rise of the LED backlight 102can be made small.

Note that the number of the LEDs 201 which is arranged over the LEDarrays 205 a to 205 c and the number of the LED arrays 205 which isattached to the backboard 203 may be determined as appropriate inaccordance with the size of the liquid crystal panel 101.

Note that although the LEDs are arranged by forming a plurality of LEDarrays in a configurational example shown in FIG. 2, the all LED whichare necessary for forming the LED backlight may be arranged over onewiring board. A configurational example of the LED backlight 102 in thiscase is shown in FIG. 4. FIG. 4 shows a plan view of the LED backlight102 when it is seen from the front surface side of the LED backlight102.

Note that in order to improve light use efficiency of the LED 201, areflecting means for reflecting light emitted from the LED 201 may bearranged. FIGS. 5A and 5B, FIGS. 6A and 6B show configurational examplesof the LED backlight 102 in this case.

Note that light use efficiency of the LED corresponds to a ratio of theamount of light which enters the liquid crystal panel with respect tothe amount of light which is radiated from the LED.

FIGS. 5A and 5B show a configurational example of the LED backlight inthe case of applying a reflecting coating 501 which is made of amaterial having high reflectivity to a backboard 203. By applying thereflecting coating 501 to the backboard 203 in this manner, thebackboard 203 can be utilized as a substitute for a reflector of the LED201. This helps light emitted from the LED 201 be reflected on thebackboard 203 to which the reflecting coating is applied, so that thelight emitted from the LED 201 enters the liquid crystal panel 101, andthus, the light use efficiency of the LED 201 can be improved.

FIGS. 6A and 6B show a configurational example of the LED backlight inthe case of additionally providing a reflecting portion which is made ofa material having high reflectivity. In FIGS. 6A and 6B, a reflectingportion 601 is arranged so as to cover the wiring board 202, theterminals 206 a and 206 b of the LED 201, or the like. This helps thelight emitted from the LED 201 be reflected on the reflecting portion601, so that the light emitted from the LED 201 enters the liquidcrystal panel 101, and thus, the light use efficiency of the LED 201 canbe improved.

Note that the reflecting portion 601 may be an optical functioning sheethaving a function of reflecting light, a material which includes copper,iron, aluminum, or the like, a metal plate of stainless steel or thelike, for example. Alternatively, a white and plastic or acrylic platemay be employed. In addition, a surface of the reflecting portion 601may have unevenness. This helps the light emitted from the LED 201 bereflected diffusely on the unevenness of the surface of the reflectingportion 601, so that the light can also be diffused. Accordingly, thelight use efficiency of the LED 201 can be improved.

Note that in order to improve the light use efficiency of the LED 201,the wiring board 202, the backboard 203, and the screw 204 may be white.Thus, the light emitted from the LED 201 is reflected more, so that thelight use efficiency of the LED 201 can be improved.

By providing the reflecting means for reflecting the light emitted fromthe LED in this manner, the light use efficiency of the LED can beimproved. In addition, particularly in the case of arranging the threecolors of LED of R, G, and B alternately, the light of three colors ofR, G, and B more easily mix with each other since the light is reflectedon the reflecting means; thereby, uniform white light can enter theliquid crystal panel 101. Accordingly, the color unevenness can bereduced.

Next, a configuration of the cooling device 103 in this embodiment modeis described with reference to FIG. 7, FIGS. 8A and 8B.

FIG. 7 shows a plan view of the cooling device 103 in this embodimentmode when it is seen from the back surface side of the LED backlight102. The cooling device 103 in this embodiment mode includes a coolant701, a pipe for the coolant (hereinafter described as a coolant pipe702), a coolant circulation pump 703, a coolant tank 704, or the like.

In addition, FIG. 8A shows a plan view of the cooling device 103 shownin FIG. 7 when it is seen from the X-axis side in FIG. 7. Further, FIG.8B shows a plan view of the cooling device 103 shown in FIG. 7 when itis seen from the Y-axis side in FIG. 7.

Note that the coolant 701 is liquid for cooling the LED backlight. Inaddition, the coolant pipe 702 is a pipe for the coolant 701. Further,the coolant circulation pump 703 is a pump for circulating the coolant701 in the cooling device. Moreover, the coolant tank 704 is a tank forstoring the coolant 701.

Note that in the case of decreasing the amount of the coolant 701, thecoolant 701 can be supplied to the coolant tank 704.

One end of the coolant pipe 702 is connected to the coolant tank 704 andthe other end of the coolant pipe 702 is connected to the coolant tank704 through the coolant circulation pump 703.

In addition, the coolant pipe 702 is arranged on the back surface sideof the LED backlight 102 and arranged so as to be in contact with theLED backlight 102 as shown in FIGS. 8A and 8B. Furthermore, in a portionwhere the coolant pipe 702 is in contact with the LED backlight 102, thecoolant pipe 702 is arranged by bending many times as shown in FIG. 7.

Note that as a method of making the LED backlight 102 and the coolantpipe 702 in contact with each other, the LED backlight 102 and thecoolant pipe 702 may simply be in contact with each other or the LEDbacklight 102 and the coolant pipe 702 may be attached together by usingan adhesive agent having high thermal conductance, an adhesive agentincluding a conductive particle, or the like.

In addition, as shown in FIG. 9A, the coolant pipe 702 may be fixed tothe LED backlight 102 by using a fixing device of coolant pipe 901. Notethat FIG. 9B shows a cross-sectional structure of the fixing device ofcoolant pipe 901. In the fixing device of coolant pipe 901, a fixingplate 902 is put on the coolant pipe 702 and the fixing plate 902 isattached to the backboard 203 of the LED backlight 102 by using screws903 a and 903 b.

Note that although the coolant circulation pump 703 and the coolant tank704 are separately arranged in this embodiment mode, the invention isnot limited to this. The coolant circulation pump 703 and the coolanttank 704 may be integrated.

Note that in order to improve the light use efficiency of the LED, areflecting portion may be arranged in the LED backlight. FIGS. 63A and63B show a configurational example of the LED backlight and the coolingdevice in this case. A reflecting portion 6301 is arranged in the LEDbacklight 102 in FIGS. 63A and 63B.

Next, an operation of the cooling device of this embodiment mode isdescribed with reference to FIG. 7.

First, the coolant 701 is poured from the coolant tank 704 into thecoolant pipe 702 by using the coolant circulation pump 703. After that,the coolant 701 is circulated in the cooling device. Then, the coolant701 which has circulated in the cooling device is stored in the coolanttank 704 again.

In this series of operations, the heat generated from the LED backlight102 is radiated by the coolant 701 and the coolant pipe 702 by makingthe coolant 701 flow to the coolant pipe 702 which is in contact withthe LED backlight 102, so that temperature of the LED backlight 102 canbe lowered. Thus, the LED backlight 102 can be cooled. In addition, inthe portion where the coolant pipe 702 is in contact with the LEDbacklight 102, the coolant pipe 702 is arranged by bending many times.Therefore, an area where the LED backlight 102 and the coolant pipe 702are in contact with each other can be increased, so that coolingefficiency of the LED backlight 102 can be more improved.

By cooling the LED backlight with the liquid cooling type coolingdevice, the LED backlight can be cooled in a shorter time and at lowertemperature compared to the case of using a conventional air-cooledcooling device, so that the cooling efficiency can be more improved.Therefore, a display defect such as display unevenness or colorunevenness caused by the heat generated from the LED backlight can bereduced.

Note that although the coolant 701 flows clockwise in FIG. 7, adirection of supplying the coolant 701 is not limited to this. Thecoolant 701 may be supplied counterclockwise.

Note that when vertical and horizontal length of the LED backlight aredenoted by L₁ and L₂ respectively and a diameter of the coolant pipe isdenoted by D (refer to FIG. 7), the diameter of the coolant pipe D ispreferably greater than or equal to 1/100 and less than or equal to 1/10of the shorter one of the vertical length L₁ and the horizontal lengthL₂ of the LED backlight. This is because when the diameter of thecoolant pipe is too long, the thickness of the cooling device isincreased, so that a lot of space is required in the cooling devicealthough a large quantity of the coolant can be supplied to the coolantpipe to improve the cooling efficiency. On the other hand, when thediameter of the coolant pipe is too short, high pressure is required tosupply the coolant to the coolant pipe so that a high-performancecoolant circulation pump has to be used although the thickness of thecooling device can be made small. Accordingly, the diameter of thecoolant pipe is required to be set within an appropriate range.

Note that although the coolant pipe 702 is arranged by bending up anddown (on the Y-axis side in FIG. 7) many times in FIG. 7, an arrangementof the coolant pipe 702 is not limited to this.

For example, the coolant pipe 702 may be arranged by bending from sideto side (on an X-axis side in FIG. 10) many times as shown in FIG. 10.In the case of arranging the coolant pipe 702 in this manner, the areawhere the LED backlight 102 and the coolant pipe 702 are in contact witheach other can be increased similarly to the case shown in FIG. 7, sothat the cooling efficiency of the LED backlight 102 can be moreimproved.

In addition, in FIG. 10, although the coolant pipe 702 is arranged so asto be in parallel to the X-axis in FIG. 10, the coolant pipe 702 may bearranged so as to have a slope to the X-axis in FIG. 11 as shown in FIG.11. FIG. 11 shows the case where by slanting with slope angles α and β,the coolant pipe 702 is arranged (note that FIG. 10 corresponds to thecase where α=β=0° is satisfied). By slanting and arranging the coolantpipe 702 in this manner, the coolant 701 is lifted to an upper part ofthe LED backlight with the coolant circulation pump 703. After that, thecoolant 701 can be supplied naturally to the coolant pipe 702 bygravity. Accordingly, load of the coolant circulation pump 703 can bereduced.

Note that the slope angles α and β of the coolant pipe 702 are both setto greater than or equal to 0° and less than or equal to 90° in FIG. 11.In addition, the slope angles α and β may be equal to each other, thatis, α=β, or may be different from each other, that is, α≠β; however, α=βis preferably employed. This is because the coolant 701 can flow moreeasily when the slope angles α and β satisfy α=β. Note that when adifference between α and β is within 10%, that is, the angle of slope αis within a range of 0.9β<α<1.1β, the slope angles α and β areconsidered to satisfy α=β.

In addition, although the coolant pipe 702 is not divided on the way inFIG. 7 to FIG. 11, the coolant pipe 702 may be divided on the way. FIGS.13 and 14 show exemplary arrangements of the coolant pipe 702 in thiscase. FIG. 13 shows an exemplary arrangement of the coolant pipe 702 inthe case of dividing the coolant pipe 702 up and down (on a Y-axis sidein FIG. 13). FIG. 14 shows an arrangement example of the coolant pipe702 in the case of dividing the coolant pipe 702 from side to side (onan X-axis side in FIG. 14). By dividing the coolant pipe 702 on the wayin this manner, the coolant 701 can be supplied in multiple directionsat one time. Therefore, many regions of the LED backlight can be cooledat one time, so that the cooling efficiency of the LED backlight 102 canbe more improved. In addition, the LED backlight can be equally cooled.

Note that when a diameter of a portion of the coolant pipe which is notdivided is denoted by D₁, and a diameter of a portion of the coolantpipe which is divided is denoted by D₂, D₁>D₂ is preferably satisfied.This is because more coolant flows in the portion of the coolant pipewhich is not divided than the portion of the coolant pipe which isdivided. By satisfying D₁>D₂, the coolant can flow more easily.

Meanwhile, the heat generated from the LED backlight easily remains in acentral portion of the LED backlight in usual, so that temperature inthe central portion of the LED backlight becomes higher than temperaturein a peripheral portion of the LED backlight. Thus, by arranging thecoolant pipe 702 in spiral and making the coolant 701 flow from acentral portion of the spiral to an outside as shown in FIG. 15,temperature can be decreased gradually from the central portion of theLED backlight having the highest temperature. Accordingly, the coolingefficiency of the LED backlight can be more improved. In addition, sincean phenomenon where temperature of the backlight is different dependingon places (temperature unevenness) can be decreased, a display defectsuch as display unevenness or color unevenness caused by the temperatureunevenness of the LED backlight can be reduced.

Note that in the case of arranging the coolant pipe 702 in spiral, thecoolant pipe 702 is arranged counterclockwise from the central portionof the spiral toward the outside in FIG. 15; however, the spiral may bearranged in reverse.

Note that the flow directions of the coolant 701 shown in FIGS. 7 to 15are not limited to the directions as illustrated. The coolant pipe maybe supplied in directions opposite to the directions as illustrated.

Note that the arrangement of the coolant pipe 702 is not limited to theaforementioned examples. In particular, when the coolant pipe 702 isprovided on a back surface side of the LED backlight 102, the coolantpipe 702 is preferably arranged such that at least one or more LEDexists over the coolant pipe 702. This is because distance between thecoolant pipe and the LED becomes closer, so that the LED can be cooledin a shorter time and more efficiently.

Note that although shapes of cross sections of the coolant pipe 702 arecircles in FIG. 7 to FIG. 15, the invention is not limited to this. Forexample, a shape of a cross section of the coolant pipe 702 may be aquadrangle.

For example, FIGS. 12A and 12B show a configurational example of thecooling device 103 when the shape of the cross section of the coolantpipe is a rectangle. In FIGS. 12A and 12B, the shape of the crosssection of the coolant pipe 702 is made to be a rectangle having roundcorners and a long side of the rectangle is in contact with the LEDbacklight 102.

By making the shape of the cross section of the coolant pipe 702rectangular and the long side of the rectangle be in contact with theLED backlight in this manner, the areas where the LED backlight and thecoolant pipe are in contact with each other can be increased so thatcooling efficiency of the LED backlight can be more improved. Inaddition, by shortening a short side of the rectangle more, thickness ofportions in which the coolant pipe takes up can be thinner. Accordingly,the display device can be thinner.

Further, by rounding the corners of the rectangle of the cross sectionof the coolant pipe, stress which is applied to the coolant pipe whenthe coolant pipe is bent can be smaller, so that the coolant pipe ishardly damaged.

It is to be noted that with respect to a degree for rounding the cornersof the rectangle of the cross section of the coolant pipe, in therectangle of the cross section of the coolant pipe, when the length ofthe short side is denoted by L₃ and the length of the long side isdenoted by L₄ (refer to FIGS. 12A and 12B), the radii of curvature inportions of the corners of the rectangle are equal to less than or equalto than half L₃.

Meanwhile, when the coolant is circulated in the cooling device, thetemperature of the coolant rises by the heat generated from the LEDbacklight. Then, the coolant of which temperature rises is stored in thecoolant tank again. Thus, in order to lower the temperature of thecoolant, a cooling fan for cooling the coolant tank may be arranged.FIG. 16 shows a configurational example of the cooling device 103 inthis case.

FIG. 16 shows the case where a cooling fan 1601 is additionally providedas a means for lowering temperature of the coolant 701 in FIG. 7. Thecooling fan 1601 is operated and wind 1602 is got on the coolant tank704, and thus, the coolant tank 704 and the coolant 701 which is storedin the coolant tank 704 are cooled. Therefore, the temperature of thecoolant 701 can be lowered so that the cooling efficiency of the LEDbacklight can be more improved.

Alternatively, a radiator may be arranged as a means for lowering thetemperature of the coolant. FIG. 17 shows a configurational example ofthe cooling device 103 in this case.

FIG. 17 shows the case where a radiator 1701 is additionally provided asa means for lowering the temperature of the coolant 701 in FIG. 7. InFIG. 17, the radiator 1701 and a cooling fan 1702 are additionallyprovided in addition to the devices shown in FIG. 7.

First, the coolant 701 which is stored in the coolant tank 704 is putthrough the radiator 1701. In the radiator 1701, the cooling fan 1702 isoperated and wind 1703 is got on the radiator 1701, and thus, thecoolant 701 which is put through the radiator 1701 is cooled. Then, thecoolant 701 which is cooled by the radiator 1701 is circulated in thecooling device by using the coolant circulation pump 703.

By using the radiator 1701 in this manner, the temperature of thecoolant 701 can be lowered in a short time so that the coolingefficiency of the LED backlight can be more improved.

Note that water, ethylene glycol, glycerin, polyvinyl alcohol solution,or the like is used as the coolant 701. Alternatively, antifreezesolution to which a corrosion inhibitor is added may be employed, ifnecessary. Note that liquid which is employed as the coolant is notlimited to the aforementioned examples.

Note that a material of the coolant pipe 702 may be one includingcopper, iron, aluminum, or the like, or metal such as stainless steelfor example, or may be an organic compound such as polyethylene,polystyrene, polypropylene, or polyester terephthalate for example.

For example, when the coolant pipe 702 is made from metal, thermalconductance is increased so that the LED backlight can be cooled moreefficiently. In particular, since copper has high thermal conductanceand corrosion resistance, copper is preferably employed in the casewhere the coolant pipe 702 is made of metal. Alternatively, when thecoolant pipe 702 is made of an organic compound, a coolant pipe havingflexibility can be formed so that the coolant pipe 702 can be arrangedfreely. Further, when a silicon-based material is employed as thematerial of the coolant pipe 702, a coolant pipe having flexibility canbe formed so that the coolant pipe 702 can be arranged freely.

Note that the material of the coolant pipe 702 is not limited to theaforementioned examples.

Note that the coolant pipe may be manufactured of one kind of material,or may be formed to have a multi-layer structure by using a plurality ofmaterials. For example, as shown in FIG. 18, the coolant pipe 702 may beformed to have a two-layer structure using two kinds of materials of afirst material 1801 and a second material 1802. In particular, by usinga material having high corrosion resistance for the first material 1801and a material having high thermal conductance for the second material1802, a coolant pipe having high resistance to the corrosion with thecoolant 701 and radiating the heat of the LED backlight efficiently canbe formed.

Note that various contents described in this embodiment mode may befreely combined and implemented.

Embodiment Mode 2

Although the entire LED backlight is cooled by using one coolant pipe inEmbodiment Mode 1, the LED backlight is divided into a plurality ofcooling regions and the LED backlight may be cooled in each coolingregion. Thus, this embodiment describes the case where the LED backlightis divided into a plurality of cooling regions and the LED backlight iscooled in each cooling region.

FIG. 20 shows a configurational example of a cooling device in thisembodiment mode.

FIG. 20 shows a plan view of the cooling device 103 in this embodimentmode when it is seen from a back surface side of the LED backlight 102.FIG. 20 shows a configurational example of the cooling device 103 in thecase where the LED backlight is divided into two cooling regions fromside to side and the LED backlight is cooled in each cooling region.

In FIG. 20, the LED backlight 102 is divided into two cooling regions ofa first cooling region 2001 a and a second cooling region 2001 b fromside to side, and coolant pipes 702 a and 702 b, coolant circulationpumps 703 a and 703 b, and coolant tanks 704 a and 704 b are arranged inthe first and second cooling regions 2001 a and 2001 b. In addition,each of the coolant pipes 702 a and 702 b is arranged by bending up anddown (on a Y-axis side in FIG. 20) many times.

By dividing the LED backlight into a plurality of cooling regions andcooling the LED backlight in each cooling region in this manner, thetime which is needed for cooling the entire LED backlight can be madeshorter than the case where the LED backlight is cooled without beingdivided into a plurality of cooling regions, so that the coolingefficiency can be more improved. In addition, temperature unevenness ofthe LED backlight can be more reduced, and a display defect such asdisplay unevenness or color unevenness caused by the temperatureunevenness of the LED backlight can be reduced.

Note that flow directions of the coolants may be all the same in aplurality of cooling regions, or may be different in each of a pluralityof cooling regions.

For example, in FIG. 20, a coolant 701 a flows counterclockwise in thefirst cooling region 2001 a and a coolant 701 b flows clockwise in thesecond cooling region 2001 b; however, the invention is not limited tothis. The coolant 701 a may flow clockwise in the first cooling region2001 a and the coolant 701 b may flow counterclockwise in the secondcooling region 2001 b. Alternatively, both of the coolants 701 a and 701b may flow clockwise or may flow counterclockwise in the first andsecond cooling regions 2001 a and 2001 b. Note that as shown in FIG. 20,when the coolant 701 a flows counterclockwise in the first coolingregion 2001 a and the coolant 701 b flows clockwise in the secondcooling region 2001 b, temperature can be decreased gradually from thecentral portion of the LED backlight where heat easily remains and ofwhich temperature rises most. Accordingly, since the cooling efficiencyof the LED backlight can be more improved and further the temperatureunevenness of the LED backlight can be more reduced, the display defectsuch as display unevenness or color unevenness caused by the temperatureunevenness of the LED backlight can be reduced.

It is to be noted that although each of the coolant pipes 702 a and 702b is arranged by bending up and down (on the Y-axis side in FIG. 20)many times in FIG. 20, an arrangement of the coolant pipes 702 a and 702b is not limited to this.

For example, as shown in FIGS. 21 and 22, each of the coolant pipes 702a and 702 b may be arranged in spiral. Note that FIG. 21 shows the casewhere each of the coolant pipes 702 a and 702 b is arrangedcounterclockwise from a central portion of the spiral toward an outsidein the first and second cooling regions 2001 a and 2001 b. In addition,FIG. 22 shows the case where the coolant pipe 702 a is arrangedclockwise from the central portion of the spiral toward the outside inthe first cooling region 2001 a and the coolant pipe 702 b is arrangedclockwise toward from the central portion of the spiral to the outsidein the second cooling region 2001 b. Note that in both of FIGS. 21 and22, the coolants 701 a and 701 b flow toward the central portions of thespirals from the outsides.

When each of the coolant pipes 702 a and 702 b is arranged in spiral inthe first and second cooling regions 2001 a and 2001 b and the coolants701 a and 701 b flow toward the central portions of the spirals from theoutsides as shown in FIG. 22, temperature can be decreased graduallyfrom the central portion of the LED backlight where heat easily remainsand of which temperature rises most similarly to the case shown in FIG.20. Accordingly, since the cooling efficiency of the LED backlight canbe more improved and further the temperature unevenness of the LEDbacklight can be more reduced, the display defect such as displayunevenness or color unevenness caused by the temperature unevenness ofthe LED backlight can be reduced.

Alternatively, for example, the arrangement of the coolant pipe may bechanged in each of a plurality of cooling regions as shown in FIG. 23.

FIG. 23 shows the case where the coolant pipe 702 a is arranged bybending up and down (on a Y-axis side in FIG. 23) many times in thefirst cooling region 2001 a and the coolant pipe 702 b is arranged bybending from side to side (on an X-axis side in FIG. 23) many times inthe second cooling region 2001 b.

In FIG. 23, by making the coolants 701 a and 701 b flow counterclockwisein the first cooling region 2001 a and making the coolants 701 a and 701b flow clockwise in the second cooling region 2001 b, temperature can bedecreased gradually from the central portion of the LED backlight whereheat easily remains and of which temperature rises most similarly to thecases shown in FIGS. 20 to 22. Accordingly, since the cooling efficiencyof the LED backlight can be more improved and further the temperatureunevenness of the LED backlight can be more reduced, the display defectsuch as display unevenness or color unevenness caused by the temperatureunevenness of the LED backlight can be reduced.

Note that although the LED backlight is divided into two cooling regionsfrom side to side in FIGS. 20 to 23, division of the cooling regions isnot limited to this example. For example, the LED backlight may bedivided into two cooling regions up and down as shown in FIG. 24.

In FIG. 24, the LED backlight 102 is divided into two cooling regions ofa first cooling region 2401 a and a second cooling region 2401 b up anddown, and the coolant pipes 702 a and 702 b, the coolant circulationpumps 703 a and 703 b, and the coolant tanks 704 a and 704 b arearranged in the first and second cooling regions 2401 a and 2401 b. Inaddition, each of the coolant pipes 702 a and 702 b are arranged bybending from side to side (on an X-axis side in FIG. 24) many times.

In FIG. 24, by making both of the coolants 701 a and 701 b flowcounterclockwise in the first and second cooling regions 2401 a and 2401b, temperature can be decreased gradually from the central portion ofthe LED backlight where heat easily remains and of which temperaturerises most similarly to the cases shown in FIGS. 20 to 23. Accordingly,since the cooling efficiency of the LED backlight can be more improvedand further the temperature unevenness of the LED backlight can be morereduced, the display defect such as display unevenness or colorunevenness caused by the temperature unevenness of the LED backlight canbe reduced.

By providing the coolant circulation pump in each of a plurality ofcooling regions and circulating the coolant as in this embodiment mode,the length of the coolant pipe per coolant circulation pump can be madeshorter than the case where the LED backlight is cooled without beingdivided into a plurality of cooling regions, and thus, the coolant canbe circulated in a shorter time. In addition, the coolant pipe can beprocessed easily.

Further, since the length of the coolant pipe per coolant circulationpump can be made shorter, cooling efficiency similar to the case wherethe LED backlight is cooled without being divided into a plurality ofcooling regions can be maintained, even if a coolant circulation pumphaving lower capability than that of the case where the entire LEDbacklight is cooled without being divided into a plurality of coolingregions. Accordingly, cost of the coolant circulation pump can bereduced.

Note that although the coolant circulation pump and the coolant tank arearranged in each of a plurality of cooling regions in this embodimentmode, the coolant circulation pump and the coolant tank may be shared ina plurality of cooling regions.

For example, FIG. 25 shows a configurational example of the coolingdevice 103 in the case where the coolant tank is shared in the first andsecond cooling regions in the case shown in FIG. 20. In FIG. 25, thecoolant which is stored in the coolant tank 704 is circulated in thefirst and second cooling regions 2001 a and 2001.b by using the coolantcirculation pumps 703 a and 703 b, and each of the first and secondcooling regions 2001 a and 2001 b is cooled.

In addition, FIG. 26 shows a configurational example of the coolingdevice 103 in the case where the coolant circulation pump and thecoolant tank are shared in the first and second cooling regions in thecase shown in FIG. 20. In FIG. 26, the coolant which is stored in thecoolant tank 704 is circulated in the first and second cooling regions2001 a and 2001 b by using the coolant circulation pump 703 to cool eachof the first and second cooling regions 2001 a and 2001 b.

By sharing the coolant circulation pump and the coolant tank in aplurality of cooling regions as shown in FIGS. 25 and 26, the number ofthe coolant circulation pumps and the coolant tanks can be smaller thanthe case where the coolant circulation pump and the coolant tank areprovided in each of a plurality of cooling regions, and thus, cost to acorresponding extent can be reduced.

By dividing the LED backlight into a plurality of cooling regions andleading the cooling of the LED backlight in each cooling region as inthis embodiment mode, the LED backlight can be cooled more efficientlyand in a shorter time than the case where the LED backlight is cooledwithout being divided into a plurality of cooling regions. Inparticular, in the case of cooling a LED backlight which is incorporatedin a large liquid crystal display, the time for cooling can be madeshorter by dividing the LED backlight into a plurality of coolingregions and cooling the LED backlight in each cooling region. Thus, thecooling efficiency can be remarkably improved and a method of dividingthe LED backlight into a plurality of cooling regions and cooling theLED backlight in each cooling region becomes a greatly effective method.Further, since the temperature unevenness of the LED backlight can bemore reduced, the display defect such as display unevenness or colorunevenness caused by the temperature unevenness of the LED backlight canbe reduced.

Note that although the case where the LED backlight is divided into twocooling regions from side to side or up and down and the LED backlightis cooled in each cooling region is shown in this embodiment mode, thenumber of the divided cooling regions is not limited to two. The coolingregion may be divided into three or more. In addition, the division ofthe cooling region is not limited to the division of side to side or upand down. The cooling region may be divided in a grid or at random.

Note that various contents described in this embodiment mode may befreely combined and implemented. In addition, the contents described inthis embodiment mode may be freely combined with the contents describedin Embodiment Mode 1 and implemented.

Embodiment Mode 3

In Embodiment Modes 1 and 2, although the cooling device is arranged onthe back surface side of the LED backlight to cool the LED backlight,the LED backlight may be cooled by arranging the cooling device on thefront surface side of the LED backlight. This embodiment describes thecase where the cooling device is arranged on the front surface side ofthe LED backlight.

First, a configuration of a display device in this embodiment mode isdescribed with reference to FIG. 19.

FIG. 19 shows a configurational example of the display device in thisembodiment mode. The display device in this embodiment mode includes theliquid crystal panel 101, the LED backlight 102, the cooling device 103,or the like. The cooling device 103 is arranged on a back surface sideof the liquid crystal panel 101 and the LED backlight 102 is arranged ona back surface side of the cooling device 103. Note that the coolingdevice 103 is arranged so as to be in contact with the LED backlight102.

Note that the cooling device 103 is arranged on the front surface sideof the LED backlight in the display device in this embodiment mode,which is a main difference from the display devices shown in EmbodimentsModes 1 and 2. That is, the cooling device 103 is arranged between theliquid crystal panel 101 and the LED backlight 102 and arranged so as tobe in contact with the LED backlight 102.

Next, configurational examples of the cooling device in this embodimentmode are described with reference to FIGS. 27 and 28.

FIG. 27 shows a plan view of the cooling device 103 in this embodimentmode when it is seen from the front surface side of the LED backlight102. In addition, FIG. 28 shows a plan view of the cooling device shownin FIG. 27 when it is seen from an X-axis side in FIG. 27.

As shown in FIGS. 27 and 28, the cooling device 103 in this embodimentmode is not arranged on the back surface side of the LED backlight butarranged on the front surface side of the LED backlight, and the coolantpipe 702 is arranged over the backboard 203 which is between theadjacent LED arrays 205 a to 205 c.

Note that as a method of making the LED backlight 102 and the coolantpipe 702 in contact with each other, the LED backlight 102 and thecoolant pipe 702 may simply be in contact with each other or the LEDbacklight 102 and the coolant pipe 702 may be attached together by usingan adhesive agent having high thermal conductance, an adhesive agentincluding a conductive particle, or the like.

In addition, the coolant pipe 702 may be fixed on the LED backlight 102by using the fixing device of coolant pipe 901 as shown in FIG. 9A. FIG.29 shows a configurational example of the cooling device 103 when thecoolant pipe is fixed by the fixing device of coolant pipe.

By arranging the coolant pipe 702 over the backboard 203 which isbetween the adjacent LED arrays 205 a to 205 c and making the coolant701 flow, cooling can be conducted in a place which is nearer to the LED201, so that the time for cooling the entire LED backlight 102 can bemade shorter, and thus, cooling efficiency can be more improved.Accordingly, the display defect such as display unevenness or colorunevenness caused by the temperature unevenness of the LED backlight canbe reduced.

By arranging the coolant pipe 702 over the backboard 203 which isbetween the adjacent LED arrays 205 a to 205 c, the thickness ofportions where the LED backlight 102 and the coolant pipe 702 areattached to each other can be thinner than the case where the coolantpipe 702 is arranged on the back surface side of the LED backlight 102.Accordingly, the thickness of the display device can be thinned.

Note that when a diameter of the coolant pipe 702 is denoted by D and aninterval between the adjacent LED arrays 205 a to 205 c is denoted by W(refer to FIG. 28), D<W is preferably employed. That is, it ispreferable that the coolant pipe 702 and the LED 201 are not in directcontact with each other. This is because when D≧W is employed, lightemitted from the LED 201 is shielded by the coolant pipe 702 and enoughlight does not enter the liquid crystal panel 101, so that colorunevenness or decrease in luminance occurs. Therefore, by employing D<W,the light emitted from the LED 201 can be prevented from being shieldedby the coolant pipe 702, and thus, the color unevenness or the decreasein the luminance can be reduced.

Note that in order to improve the light use efficiency of the LED, areflecting coating which is made of a material having high reflectivitymay be applied to the coolant pipe 702. FIG. 30 shows a configurationalexample of the cooling, device in this case.

In FIG. 30, by applying a reflecting coating 3001 to the coolant pipe702, the coolant pipe 702 can be utilized as a substitute for areflector of the LED 201.

By applying the reflecting coating 3001 to the coolant pipe 702 in thismanner, the light use efficiency of the LED can be improved so that muchlight can enter the liquid crystal panel 101. In addition, since thecoolant pipe has a curved surface, the light emitted from the LED isreflected in more directions. Therefore, in the case of arranging threecolors of LEDs of R, G, and B alternately, the light of three colors ofR, G, and B more easily mix with each other; thereby, uniform whitelight can enter the liquid crystal panel 101. Accordingly, the colorunevenness can be reduced.

Alternatively, in order to improve the light use efficiency of the LED,a reflecting portion may be arranged in the LED backlight as shown inEmbodiment Mode 1 (FIGS. 6A and 6B). In this case, the coolant pipe 702may be arranged in a region which is sandwiched between the backboard203 which is between the adjacent LED arrays 205 a to 205 c and thereflecting portion. FIG. 31 shows a configurational example of thecooling device 103 in this case.

In FIG. 31, the coolant pipe 702 is arranged in a region which issandwiched between the backboard 203 which is between the adjacent LEDarrays 205 a to 205 c and a reflecting portion 3101.

Note that as a method of making the coolant pipe 702 and the reflectingportion 3101 in contact with each other, the coolant pipe 702 and thereflecting portion 3101 may be directly in contact with each other, orthe coolant pipe 702 and the reflecting portion 3101 may be attachedtogether by using an adhesive agent having high thermal conductance, anadhesive agent including a conductive particle, or the like.

By additionally providing the reflecting portion 3101 in this manner,the light use efficiency of the LED can be improved, and thus, muchlight can enter the liquid crystal panel 101. In particular, in the casewhere the reflecting portion 3101 is formed of metal having high thermalconductance (e.g., one including copper, iron, aluminum, or the like, orstainless steel), the reflecting portion 3101 is cooled by the coolant701 so that the cooling efficiency of the LED backlight 102 can be moreimproved.

It is to be noted that in FIG. 31, the LED arrays 205 a to 205 c areattached to the backboard 203 by using the screw 204; however, the LEDarrays 205 a to 205 c may be attached to the reflecting portion 3101after removing the backboard 203 when the reflecting portion 3101 isadditionally provided. FIG. 32 shows a configurational example of thecooling device 103 in this case.

In FIG. 32, the LED arrays 205 a to 205 c is attached to the reflectingportion 3101 by using a screw 3201. In addition, the coolant pipe 702 isarranged between the adjacent LED arrays 205 a to 205 c so as to be incontact with the reflecting portion 3101.

By attaching the LED arrays 205 a to 205 c to the reflecting portion3101 in this manner, the backboard 203 can be removed so that the numberof components can be reduced, and thus, cost can be reduced.

Note that the reflecting portion 3101 may be an optical functioningsheet having a function of reflecting light, a material which includescopper, iron, aluminum, or the like, or a metal plate of such asstainless steel, for example. Alternatively, a white and plastic oracrylic plate may be employed.

Note that each surface of the coolant pipe 702, the backboard 203, andthe reflecting portion 3101 may have unevenness. This helps the lightemitted from the LED 201 be reflected diffusely on the unevenness ofeach surface of the coolant pipe 702, the backboard 203, and thereflecting portion 3101, so that the light can also be diffused.Accordingly, the light use efficiency of the LED 201 can be improved.

Note that the coolant pipe may be arranged on both of the front surfaceside and the back surface side of the LED backlight. FIG. 33 shows aconfigurational example of the LED backlight and the cooling device inthis case.

FIG. 33 shows a cross-sectional view of the LED backlight and thecooling device in the case of arranging the coolant pipe on both of thefront surface side and the back surface side of the LED backlight. Onthe front surface side of the LED backlight 102, a coolant pipe 702 c isarranged in the backboard 203 which is between the adjacent LED arrays205 a to 205 c as described in this embodiment mode. In addition, on theback surface side of the LED backlight 102, a coolant pipe 702 d isarranged so as to be in contact with the backboard 203 as shown inEmbodiment Mode 1. In FIG. 33, an example where the coolant pipe 702 dwhich is arranged on the back surface side of the LED backlight 102 isarranged by bending up and down (on a Y-axis side in FIG. 33) many timesas shown in FIG. 7 is shown.

By arranging the coolant pipe on both of the front surface side and theback surface side of the LED backlight, the LED backlight can be cooledfrom both of the front surface side and the back surface side, and thus,the cooling efficiency can be more improved.

Note that an arrangement of the coolant pipe 702 d which is arranged onthe back surface side of the LED backlight 102 is not limited to bendingup and down many times. The coolant pipe 702 d which is arranged on theback surface side of the LED backlight 102 may be arranged by bendingfrom side to side (on an X-axis side in FIG. 33) many times, or may bearranged in spiral. The contents which described in Embodiment Mode 1may be applied.

Note that with respect to the coolant circulation pump and the coolanttank, different coolant circulation pumps and coolant tanks may beprovided on the front surface side and the back surface side of the LEDbacklight, or common coolant circulation pump and coolant tank may beprovided on the front surface side and the back surface side of the LEDbacklight.

Note that in order to improve the light use efficiency of the LED, areflecting portion may be arranged in the LED backlight as shown in FIG.31. FIG. 34 shows a configurational example of the LED backlight and thecooling device in this case.

In FIG. 34, the coolant pipe 702 c is arranged in a region which issandwiched between the backboard 203 which is between the adjacent LEDarrays 205 a to 205 c and a reflecting portion 3101.

By additionally providing the reflecting portion 3101 in this manner,the light use efficiency of the LED can be improved, and thus, muchlight can enter the liquid crystal panel 101. In particular, in the casewhere the reflecting portion 3101 is formed of metal having high thermalconductance (e.g., one including copper, iron, aluminum, or the like, orstainless steel), the reflecting portion 3101 is cooled by the coolant701 so that the cooling efficiency of the LED backlight 102 can be moreimproved.

Note that various contents described in this embodiment mode may befreely combined and implemented. In addition, the contents described inthis embodiment mode may be freely combined with the contents describedin Embodiment Modes 1 and 2 and implemented.

Embodiment Mode 4

This embodiment describes the case where a coolant pipe which is formedfrom a material having conductivity is utilized as an electrode forapplying a voltage to the LED forming the LED backlight.

A configuration of a display device in this embodiment mode is describedwith reference to FIG. 35, and FIGS. 36A and 36B.

FIG. 35 shows a plan view of the cooling device 103 in this embodimentmode when it is seen from the back surface side of the LED backlight102. Unlike the cooling device shown in FIG. 7, the cooling device 103shown in FIG. 35 has a configuration where the coolant pipe 702 and apower supply line 3501 are connected.

In this embodiment mode, the coolant pipe 702 is formed from a materialhaving conductivity. Note that a material having high conductivity ispreferably employed as a material of the coolant pipe 702. For example,a material which includes copper, iron, aluminum, or the like, or metalsuch as stainless steel is preferably employed. In particular, sincecopper has high thermal conductance and corrosion resistance, copper ispreferably employed as the material of the coolant pipe 702.

FIG. 36A shows a plan view of the cooling device 103 shown in FIG. 35when it is seen from an X-axis side in FIG. 35. In addition, FIG. 36Bshows a plan view of the cooling device 103 shown in FIG. 35 when it isseen from a Y-axis side in FIG. 35.

As shown in FIGS. 36A and 36B, one of terminals 206 a and 206 b of theLED 201 (the terminal 206 b in FIGS. 36A and 36B) is connected to thecoolant pipe 702. In addition, in the wiring board 202 and the backboard203, an opening 3601 for leading the terminal 206 b of the LED 201 isprovided in advance.

Note that as a method of connecting the terminal 206 b of the LED 201and the coolant pipe 702, the terminal 206 b of the LED 201 and, thecoolant pipe 702 may be connected by using solder, or an anisotropicconductive film (Anisotropic Conductive Film: ACF).

Then, by connecting the coolant pipe 702 and the power supply line 3501and applying a voltage V₀ which is in the power supply line 3501, thevoltage V₀ can be applied to the terminal 206 b of the LED 201.

The coolant pipe 702 can be utilized as an electrode for applying avoltage to the LED 201 in this manner.

By utilizing the coolant pipe 702 as the electrode for applying voltageto the LED 201 in this manner, a common voltage V₀ can easily be appliedto all of the LEDs 201 forming the LED backlight 102. In addition, awire for applying the common voltage V₀ to the all of the LEDs 201forming the LED backlight 102 is not needed to be additionally arranged.Further, since a uniform voltage can be applied to the all of the LEDs201 forming the LED backlight 102, luminance unevenness between the LEDs201 can be reduced.

In addition, by utilizing the coolant pipe 702 as the electrode forapplying voltage to the LED 201, the area of the electrode for applyingthe voltage to the LED 201 is increased, and thus, resistance of theelectrode for applying the voltage to the LED 201 can be decreased.Accordingly, heat generated by current flowing to the coolant pipe 702(Joule heat) can be suppressed and the heat generated from the LED 201can also be suppressed. Further, power consumption of the LED backlight102 can be reduced.

In addition, by supplying the coolant 701 to the coolant pipe 702, thetime for cooling the LED backlight 102 can be made shorter, and thus,the cooling efficiency of the LED backlight 102 can be more improved.

Further, since the coolant 701 flows through the coolant pipe 702, thetemperature of the coolant pipe is lowered. Thus, the resistance of thecoolant pipe 702 which is formed from the material having conductivitycan be decreased. Accordingly, the heat generated by making current flowto the coolant pipe 702 (Joule heat) can be suppressed and the heatgenerated from the LED 201 can also be suppressed. Further, the powerconsumption of the LED backlight 102 can be reduced.

In addition, since the resistance of the coolant pipe 702 which isformed from the material having conductivity can be decreased, voltagedrop caused by making current flow to the coolant pipe 702 can besuppressed. Accordingly, since variation in voltages which are appliedto the LED 201 can be suppressed, the luminance unevenness of the LEDs201 can also be reduced.

Note that the voltage V₀ which is applied to the coolant pipe 702 may bea voltage which is applied on a cathode side of the LED, or may be avoltage which is applied to an anode side of the LED. When three colorsof LEDs of R, G, and B are arranged as the LEDs 201, a voltage betweenthe anode and the cathode which is applied to the LED is differentbetween the colors of R, G, and B. Then, when the voltage V₀ which isapplied to the coolant pipe 702 is the voltage which is applied on thecathode side of the LED, a common voltage can be applied on the cathodesides in the all of the LEDs. Note that the voltage which is applied tothe anode side of the LED is different in each of R, G, and B. On theother hand, when the voltage V₀ which is applied to the coolant pipe 702is the voltage which is applied to the anode side of the LED, a commonvoltage can be applied on the anode sides in the all of the LEDs. Notethat the voltage which is applied to the cathode side of the LED isdifferent in each of R, G, and B.

In addition, by setting the voltage V₀ which is applied to the coolantpipe 702 to ground voltage, electrostatic shielding of the LED backlight102 can be conducted. That is, the coolant pipe 702 can be utilized as ashield for electrostatic shielding. Thus, an influence of anelectromagnetic wave or the like on the LED backlight 102 is eliminated,so that a malfunction or the like of the TED backlight 102 can beprevented. Further, an influence of noise on the liquid crystal panel101 can be eliminated.

It is to be noted that as the power supply line 3501, a wire which isarranged in the liquid crystal panel 101 itself may be utilized, or awire arranged in a driver circuit board where a power supply or acontroller which is necessary for driving the liquid crystal panel 101,a driver circuit for driving the LED backlight 102, or the like isarranged may be utilized. Alternatively, a ground line of the displaydevice may be utilized.

It is to be noted that although the terminal 206 b of the LED 201 isdirectly connected to the coolant pipe 702 in FIGS. 36A and 36B, themethod of connecting the terminal 206 b of the LED 201 and the coolantpipe 702 is not limited to this. For example, the terminal 206 b of theLED 201 may be connected to the coolant pipe 702 through a differentwire. FIGS. 37A and 37B show a configurational example of the LEDbacklight 102 and the cooling device 103 in this case.

FIG. 37A shows a plan view of the cooling device 103 shown in FIG. 35when it is seen from an X-axis side in FIG. 35. In addition, FIG. 37Bshows a plan view of the cooling device 103 shown in FIG. 35 when it isseen from a Y-axis side in FIG. 35.

In the configurational example shown in FIGS. 37A and 37B, a common wire3701 for connecting the terminal 206 b of the LED 201 to the wiringboard 202 for forming the LED arrays 205 a to 205 c is provided. Then,the terminal 206 b of the LED 201 which is arranged over the LED arrays205 a to 205 c is connected to the common wire 3701, and further, thecommon wire 3701 is connected to the coolant pipe 702. In addition, inthe wiring board 202 and the backboard 203, an opening 3702 for leadingthe common wire 3701 is provided in advance.

The terminal 206 b of the LED 201 and the coolant pipe 702 are connectedthrough the common wire 3701 in this manner.

Note that although the common wire 3701 is connected to the coolant pipe702 by leading the wiring board 202 and the backboard 203 in FIGS. 37Aand 37B, the invention is not limited to this. The common wire 3701 maybe connected to the coolant pipe 702 without leading the wiring board202 and the backboard 203. FIGS. 38A and 38B show a configurationalexample of the LED backlight 102 and the cooling device 103 in thiscase.

In FIGS. 38A and 38B, the common wire 3701 and the coolant pipe 702 areconnected by using an external wire 3801. Thus, the opening 3702 forleading the common wire 3701 is not needed to be provided in the wiringboard 202 and the backboard 203, so that a step of processing the wiringboard 202 and the backboard 203 can be omitted.

By connecting terminal 206 b of the LED 201 and the coolant pipe 702 bythe common wire 3701 in this manner, the opening 3601 for leading theterminal 206 b of the LED 201 is not needed to be provided in the wiringboard 202 and the backboard 203, so that the step of processing thewiring board 202 and the backboard 203 can be omitted. In addition, theterminal 206 b of the LED 201 is only necessary to be connected to thecommon wire 3701 which is over the wiring board 202, so that anarrangement and connection of the terminal 206 b of the LED 201 can beeasily conducted.

Further, since connection of the common wire 3701 and the coolant pipe702 can be easily conducted no matter how the coolant pipe 702 isarranged, connection of the terminal 206 b of the LED 201 and thecoolant pipe 702 can be conducted more easily.

Note that the arrangement of the coolant pipe 702, the flow direction ofthe coolant 701, and the like are not limited to the contents describedin FIG. 35. The contents described in Embodiment Mode 1 may be applied.

It is to be noted arrangement of the coolant pipe which is formed fromthe material having conductivity is on the back surface side of the LEDbacklight is described in this embodiment mode; however, the coolantpipe which is formed from the material having conductivity may bearranged on the front surface side of the LED backlight. FIG. 39 shows aconfigurational example of the LED backlight and the cooling device inthis case.

FIG. 39 shows a cross-sectional view of the LED backlight and thecooling device in the case where the coolant pipe which is formed fromthe material having conductivity is arranged on the front surface sideof the LED backlight. The coolant pipe 702 is arranged in the backboard203 which is between the adjacent LED arrays 205 a to 205 c as describedin Embodiment Mode 3. In addition, the coolant pipe 702 is connected tothe power supply line 3501 and the voltage V₀ of the power supply line3501 is applied.

In the configurational example shown in FIG. 39, the common wire 3701for connecting the terminal 206 b of the LED 201 to the wiring board 202forming the LED arrays 205 a to 205 c is provided. Then, the terminal206 b of the LED 201 which is arranged over the LED arrays 205 a to 205c is connected to the common wire 3701, and further, the common wire3701 is connected to the coolant pipe 702 by using the external wire3801.

By employing the aforementioned configurations, the coolant pipe 702 canbe utilized as the electrode for applying voltage to the LED 201.

In addition, a method of connecting the LED 201 and the coolant pipe 702is not limited to the method shown in FIG. 39; however, the LED 201 andthe coolant 702 can be easily connected when the common wire 3701 andthe external wire 3801 are used as shown in FIG. 39.

Further, the coolant pipe which is formed from the material havingconductivity may be arranged on both of the front surface side and theback surface side of the LED backlight. FIG. 40 shows a configurationalexample of the LED backlight and the cooling device in this case.

FIG. 40 shows a cross-sectional view of the LED backlight and thecooling device in the case where the coolant pipe which is formed fromthe material having conductivity is arranged on both of the frontsurface side and the back surface side of the LED backlight. As shown inFIG. 33, the coolant pipe 702 c which is arranged on the front surfaceside of the LED backlight is arranged over the backboard 203 which isbetween the adjacent LED arrays 205 a to 205 c. The coolant pipe 702 dwhich is arranged on the back surface side of the LED backlight isarranged so as to be in contact with the backboard 203 as shown inEmbodiment Mode 1. In FIG. 40, an example where the coolant pipe 702 dwhich is arranged on the back surface side of the LED backlight isarranged by bending up and down (on a Y-axis side in FIG. 40) many timesas shown in FIG. 7 is shown.

The coolant pipe 702 c is connected to the power supply line 3501 andthe voltage V₀ of the power supply line 3501 is applied to the coolantpipe 702 c.

In the configurational example shown in FIG. 40, the common wire 3701for connecting the terminal 206 b of the LED 201 is provided over thewiring board 202 for forming the LED arrays 205 a to 205 c. Then, theterminal 206 b of the LED 201 which is arranged over the LED arrays 205a to 205 c is connected to the common wire 3701, and further, the commonwire 3701 is connected to the coolant pipe 702 c by using the externalwire 3801.

In addition, the coolant pipe 702 c which is arranged on the frontsurface side of the LED backlight and the coolant pipe 702 d which isarranged on the back surface side of the LED backlight are connected byusing a coolant pipe-connecting wire 4001.

By employing the aforementioned configurations, the coolant pipe 702 canbe utilized as the electrode for applying voltage to the LED 201.

Note that a method of connecting the LED 201 and the coolant pipes 702 cand 702 d is not limited to the method shown in FIG. 40; however, theLED 201 and the coolant pipes 702 c and 702 d can be easily connectedwhen the common wire 3701, the external wire 3801, the coolantpipe-connecting wire 4001, or the like are employed as shown in FIG. 40.

Note that the coolant pipe 702 d which is arranged on the back surfaceside of the LED backlight and the power supply line 3501 may beconnected.

It is to be noted that in FIG. 40, the coolant pipe 702 c which isarranged on the front surface side of the LED backlight and the coolantpipe 702 d which is arranged on the back surface side of the LEDbacklight are connected by using the coolant pipe-connecting wire 4001;however, the coolant pipe 702 c and the coolant pipe 702 d are notrequired to be connected.

For example, one of coolant pipe 702 c and the coolant pipe 702 d andthe power supply line 3501 are connected, and the coolant pipe connectedto the power supply line 3501 and the terminal 206 b of the LED 201 areconnected by using the common wire 3701, and thus, the coolant pipeconnected to the power supply line 3501 can also be utilized as theelectrode for applying voltage to the LED 201. In addition, the coolantpipe which is not connected to the power supply line 3501 can beutilized to cool the LED backlight.

By employing the coolant pipe which is formed from the material havingconductivity as this embodiment mode, the coolant pipe can be utilizedas the electrode for applying voltage to the LED, and thus, the heatgenerated from the LED can be suppressed and the power consumption ofthe LED backlight can be reduced. In addition, the coolant pipe can beutilized as the shield for electrostatic shielding of the LED backlightand the influence of the electromagnetic wave or the like on the LEDbacklight is removed, so that the malfunction or the like of the LEDbacklight can be prevented. Further, since a particular device or a wirefor realizing each of these advantageous effects is not needed to beadditionally provided, the number of the components can be reduced.

Note that various contents described in this embodiment mode may befreely combined and implemented. In addition, the contents described inthis embodiment mode may be freely combined with the contents describedin Embodiment Modes 1 to 3 and implemented.

Embodiment Mode 5

In Embodiments Modes 1, 2, and 4, although the cooling device isarranged on the back surface side of the LED backlight, a thermalconductor may be arranged between the LED backlight and the coolingdevice in order to more improve the cooling efficiency of the LEDbacklight. This embodiment describes the case where the thermalconductor is arranged between the LED backlight and the cooling device.

First, a configuration of a display device in this embodiment mode isdescribed with reference to FIG. 41.

FIG. 41 shows a configurational example of the display device in thisembodiment mode. The display device in this embodiment mode includes theliquid crystal panel 101, the LED backlight 102, the cooling device 103,a thermal conductor 4101, or the like. The LED backlight 102 is arrangedon the back surface side of the liquid crystal panel 101, the thermalconductor 4101 is arranged on the back surface side of the LED backlight102, and the cooling device 103 is arranged on a back surface side ofthe thermal conductor 4101. Note that the cooling device 103 is arrangedso as to be in contact with the thermal conductor 4101.

Note that the thermal conductor 4101 is preferably a material havinghigh thermal conductance. For example, a material which includes copper,iron, aluminum, or the like, or metal such as stainless steel ispreferably employed. In particular, since copper has high thermalconductance and corrosion resistance, a plate which is formed fromcopper is preferably employed as the thermal conductor 4101.

Next, a configuration of the LED backlight 102 in this embodiment modeis described with reference to FIGS. 42A and 42B.

FIG. 42A shows a plan view of the LED backlight 102 in this embodimentmode when it is seen from an X-axis side in FIG. 41. Further, FIG. 42Bshows a plan view of the LED backlight 102 in this embodiment mode whenit is seen from a Y-axis side in FIG. 41.

The LED backlight 102 in this embodiment mode includes the LED 201, thewiring board 202, the backboard 203, the screw 204, the thermalconductor 4101, a screw 4201, or the like. In this embodiment mode, byattaching the thermal conductor 4101 to the LED backlight 102, thethermal conductor 4101 is arranged between the LED backlight 102 and thecooling device 103. In the configurational example of the LED backlight102 shown in FIGS. 42A and 42B, the thermal conductor 4101 is arrangedon a back surface side of the backboard 203 of the LED backlight 102 andthe thermal conductor 4101 is attached to the backboard 203 by using thescrew 4201.

Note that the thermal conductor 4101 may be arranged by attaching thebackboard 203 and the thermal conductor 4101 together by using anadhesive agent having high thermal conductance.

In addition, in order to improve the light use efficiency of the LED201, a reflecting means for reflecting the light emitted from the LED201 may be provided. For example, a reflecting coating which is made ofa material having high reflectivity may be applied to the backboard 203,or a reflecting portion which is made of a material having highreflectivity may be additionally provided. FIGS. 43A and 43B and FIGS.44A and 44B show a configurational example of the LED backlight 102 inthis case.

FIGS. 43A and 43B show a configurational example of the LED backlight inthe case where a reflecting coating which is made of a material havinghigh reflectivity is applied to the backboard. In FIGS. 43A and 43B, byapplying a reflecting coating 4301 to the backboard 203, the backboard203 can be utilized as a substitute for the reflector of the LED 201.

FIGS. 44A and 44B show a configurational example of the LED backlight inthe case of additionally providing a reflecting portion which is made ofa material having high reflectivity. In FIGS. 44A and 44B, a reflectingportion 4401 is arranged so as to cover the wiring board 202, theterminals 206 a and 206 b of the LED 201, or the like.

By providing the reflecting means for reflecting the light emitted fromthe LED 201 in this manner, light emitted from the LED 201 is reflectedon the reflecting means and enters the liquid crystal panel 101, andthus, the light use efficiency of the LED 201 can be improved.

Note that the reflecting portion 4401 may be an optical functioningsheet having a function of reflecting light, a material which includescopper, iron, aluminum, or the like, a metal plate of stainless steel orthe like, for example. Alternatively, a white and plastic or acrylicplate may be employed. In addition, a surface of the reflecting portion4401 may have unevenness. This helps the light emitted from the LED 201be reflected diffusely on the unevenness of the surface of thereflecting portion 4401, so that the light can also be diffused.Accordingly, the light use efficiency of the LED 201 can be improved.

Note that in order to improve the light use efficiency of the LED 201,the wiring board 202, the backboard 203, and the screws 204 and 4201 maybe white. Thus, the light emitted from the. LED 201 is reflected more,so that the light use efficiency of the LED 201 can be improved.

Next, a configuration of the cooling device 103 in this embodiment modeis described with reference to FIG. 45, and FIGS. 46A and 46B.

FIG. 45 shows a diagram of the cooling device 103 in this embodimentmode when it is seen from the back surface side of the LED backlight102. The cooling device 103 in this embodiment mode is arranged on theback surface side of the thermal conductor 4101, which is different fromthe contents described in Embodiment Modes 1, 2, and 4.

FIG. 46A shows a plan view of the cooling device 103 shown in FIG. 45when it is seen from an X-axis side in FIG. 45. In addition, FIG. 46Bshows a plan view of the cooling device 103 shown in FIG. 45 when it isseen from a Y-axis side in FIG. 45.

In this embodiment mode, by supplying the coolant 701 to the coolantpipe 702 which is arranged so as to be in contact with the thermalconductor 4101 as shown in FIGS. 46A and 46B, the thermal conductor 4101is cooled. Here, by using a material having high thermal conductance asthe thermal conductor 4101, the thermal conductor 4101 is cooled in ashorter time. Then, the LED backlight 102 is cooled through the thermalconductor 4101 which has been cooled.

By arranging the thermal conductor 4101 between the LED backlight 102and the cooling device 103 and cooling the LED backlight 102 through thethermal conductor 4101 in this manner, the time which is needed forcooling the LED backlight 102 can be made shorter than the case wherethe LED backlight is directly cooled. Therefore, the cooling efficiencyof the T ED backlight 102 can be more improved. Accordingly, the displaydefect such as display unevenness or color unevenness caused by thetemperature unevenness of the LED backlight can be reduced.

It is to be noted that the arrangement of the coolant pipe 702, the flowdirection of the coolant 701 and the like, are not limited to thecontents described in FIG. 45. The contents described in Embodiment Mode1 may be applied.

Note that when a material having high thermal conductance andconductivity (e.g., one including copper, iron, aluminum, or the like,or metal such as stainless steel) is used as the thermal conductor 4101,the thermal conductor 4101 can be utilized as an electrode for applyingvoltage to the LED 201 in the case of connecting one of the terminals206 a and 206 b of the LED 201 to the thermal conductor 4101 andapplying a certain voltage to the thermal conductor 4101. FIG. 47, andFIGS. 48A and 48B show a configurational example of the LED backlightand the cooling device in this case.

FIG. 47 shows a plan view of the cooling device 103 in this embodimentmode when it is seen from the back surface side of the LED backlight102. The cooling device 103 in this embodiment mode connects the thermalconductor 4101 and a power supply line 4701 with each other in thecooling device shown in FIG. 45.

FIG. 48A shows a plan view of the cooling device 103 shown in FIG. 47when it is seen from an X-axis side in FIG. 47. In addition, FIG. 48Bshows a plan view of the cooling device 103 shown in FIG. 47 when it isseen from a Y-axis side in FIG. 47.

As shown in FIGS. 48A and 48B, one of the terminals 206 a and 206 b ofthe

LED 201 (the terminal 206 b in FIGS. 48A and 48B) is connected to thethermal conductor 4101. In addition, in the wiring board 202 and thebackboard 203, an opening 4801 for leading the terminal 206 b of the LED201 is provided in advance.

Note that as a method of connecting the terminal 206 b of the LED 201and the thermal conductor 4101, the terminal 206 b of the LED 201 andthe thermal conductor 4101 may be connected by using solder, or ananisotropic conductive film (ACF).

Then, by connecting the thermal conductor 4101 and the power supply line4701 and applying a voltage V₀ which is in the power supply line 4701,the voltage V₀ can be applied to the terminal 206 b of the LED 201.

The thermal conductor 4101 can be utilized as the electrode for applyingvoltage to the LED 201 in this manner.

By utilizing the thermal conductor 4101 as the electrode for applyingvoltage to the LED 201 in this manner, the terminals 206 b are connectedto the same thermal conductor 4101 in all of the LEDs 201 forming theLED backlight 102. Accordingly, a common voltage V₀ can be applied toone of the terminals 206 b of the all of the LED 201. In addition, awire for applying the common voltage V₀ to the all of the LEDs 201forming the LED backlight 102 is not necessary to be additionallyprovided. Further, since a uniform voltage can be applied to the all ofthe LEDs 201 forming the LED backlight 102, the luminance unevenness ofthe LEDs 201 can be reduced.

In addition, by cooling the thermal conductor 4101 by using the coolantpipe 702, the time for cooling the LED backlight 102 can be madeshorter, and thus, the cooling efficiency of the LED backlight 102 canbe more improved.

Further, by cooling the thermal conductor 4101, resistance of thethermal conductor 4101 can be decreased. Accordingly, heat generated bymaking current flow the thermal conductor 4101 (Joule heat) can besuppressed and the heat generated from the LED backlight 102 can also besuppressed. Further, the power consumption of the LED backlight 102 canbe reduced.

In addition, since the resistance of the thermal conductor 4101 can bedecreased, voltage drop caused by supplying current to the thermalconductor 4101 can be suppressed. Accordingly, since variation in thevoltages which are applied to the LED 201 can be suppressed, theluminance unevenness of the LEDs 201 can also be reduced.

Note that the voltage V₀ which is applied to the thermal conductor 4101may be a voltage which is applied on the cathode side of the LED, or maybe a voltage which is applied to the anode side of the LED. In the casewhere three colors of LEDs of R, G, and B are arranged as the LEDs 201,a voltage between the anode and the cathode which is applied to the LEDis different between the colors of R, G, and B. Then, when the voltageV₀ which is applied to the thermal conductor 4101 is the voltage whichis applied on the cathode side of the LED, a common voltage can beapplied on the cathode sides in the all of the LEDs. Note that thevoltage which is applied to the anode side of the LED is different ineach of R, and B. On the other hand, when the voltage V₀ which isapplied to the thermal conductor 4101 is the voltage which is applied tothe anode side of the LED, a common voltage can be applied on the anodesides in the all of the LEDs. Note that the voltage which is applied tothe cathode side of the LED is different in each of R, G, and B.

In addition, by setting the voltage V₀ which is applied to the thermalconductor 4101 to ground voltage, the electrostatic shielding of the LEDbacklight 102 can be conducted. That is, the thermal conductor 4101 canbe utilized as a shield for electrostatic shielding. Thus, the influenceof the electromagnetic wave or the like on the LED backlight 102 iseliminated, so that the malfunction or the like of the LED backlight 102can be prevented. Further, the influence of noise on the liquid crystalpanel 101 can be removed.

In addition, as the power supply line 4701, a wire which is provided inthe liquid crystal panel 101 itself may be utilized, or a wire arrangedin the driver circuit board where the power supply or the controllerwhich is necessary for driving the liquid crystal panel 101, the drivercircuit for driving the LED backlight 102, or the like is arranged maybe utilized. Alternatively, a ground line of the display device may beutilized.

It is to be noted that the terminal 206 b of the LED 201 is directlyconnected to the thermal conductor 4101 in FIGS. 48A and 48B; however,the method of connecting the terminal 206 b of the LED 201 and thethermal conductor 4101 is not limited to this. For example, the terminal206 b of the. LED 201 may be connected to the thermal conductor 4101through a different wire. FIGS. 49A and 49B show a configurationalexample of the LED backlight 102 and the cooling device 103 in thiscase.

FIG. 49A shows a plan view of the cooling device 103 shown in FIG. 47when it is seen from an X-axis side in FIG. 47. In addition, FIG. 49Bshows a plan view of the cooling device 103 shown in FIG. 47 when it isseen from a Y-axis side in FIG. 47.

In the configurational example shown in FIGS. 49A and 49B, a common wire4901 for connecting the terminal 206 b of the LED 201 to the wiringboard 202 for forming the LED arrays 205 a to 205 c is provided. Then,the terminal 206 b of the LED 201 which is arranged over the LED arrays205 a to 205 c is connected to the common wire 4901, and further, thecommon wire 3701 is connected to the thermal conductor 4101. It is to benoted that in the wiring board 202 and the backboard 203, an opening4902 for leading the common wire 4901 is provided in advance.

The terminal 206 b of the LED 201 and the thermal conductor 4101 areconnected through the common wire 4901 in this manner.

Note that although the common wire 4901 is connected to the thermalconductor 4101 by leading the wiring board 202 and the backboard 203 inFIGS. 49A and 49B, the invention is not limited to this. The common wire4901 may be connected to the thermal conductor 4101 without leading thewiring board 202 and the backboard 203. FIGS. 50A and 50B show aconfigurational example of the LED backlight 102 and the cooling device103 in this case.

In FIGS. 50A and 50B, the common wire 4901 and the thermal conductor4101 are connected by using an external wire 5001. Thus, the opening4902 for leading the common wire 4901 is not needed to be provided inthe wiring board 202 and the backboard 203, so that the step ofprocessing the wiring board 202 and the backboard 203 can be omitted.

By connecting terminal 206 b of the LED 201 and the thermal conductor4101 through the common wire 4901 in this manner, the opening 4801 forleading the terminal 206 b of the LED 201 is not needed to be providedin the wiring board 202 and the backboard 203, so that the step ofprocessing the wiring board 202 and the backboard 203 can be omitted. Inaddition, the terminal 206 b of the LED 201 is only necessary to beconnected to the common wire 4901 which is over the wiring board 202, sothat an arrangement and connection of the terminal 206 b of the LED 201can be easily conducted.

Note that in the case where the coolant pipe is formed from a materialhaving conductivity, the coolant pipe can also be utilized as theelectrode for applying voltage to the LED in addition to the thermalconductor.

For example, forming the coolant pipe from a material havingconductivity is described in FIGS. 48A and 48B. In FIGS. 48A and 48B,the thermal conductor 4101 and the power supply line 4701 are connectedas well as the terminal 206 b of the LED 201 is connected to the thermalconductor 4101, and the voltage V₀ of the power supply line 4701 isapplied, and thus, the voltage V₀ can be applied to the terminal 206 bof the LED 201.

At this time, the thermal conductor 4101 and the coolant pipe 702 areattached together by using solder, the anisotropic conductive film(ACF), an adhesive agent including a conductive particle, or the like.Thus, the voltage V₀ is applied to the thermal conductor 4101 and thecoolant pipe 702.

By applying the voltage V₀ to the thermal conductor 4101 and the coolantpipe 702, the thermal conductor 4101 and the coolant pipe 702 can beutilized as electrodes for applying voltage to the LED 201. In addition,by applying the same voltage to the thermal conductor 4101 and thecoolant pipe 702, the area of the electrodes for applying the voltage tothe LED 201 is increased, and thus, resistance of the electrodes whichapply the voltage to the LED 201 can be decreased. Accordingly, the heatgenerated by flowing the current to the coolant pipe 702 (Joule heat)can be suppressed and the heat generated from the LED 201 can also besuppressed. Further, the power consumption of the LED backlight 102 canbe reduced.

Note that the power supply line 4701 may be connected to the thermalconductor 4101 or may be connected to the coolant pipe 702.

Note that the terminal 206 b of the LED 201 may be connected to thethermal conductor 4101 or may be connected to the coolant pipe 702. Asthe method of connecting the terminal 206 b of the LED 201 and thethermal conductor 4101 or the coolant pipe 702, the terminal 206 b ofthe LED 201 and the thermal conductor 4101 may be directly connected ormay be connected by using the common wire as shown in FIGS. 48A and 48B.In addition, in the case of connecting with each other by using thecommon wire, the common wire and the thermal conductor 4101 or thecoolant pipe 702 may be directly connected as shown in. FIGS. 49A and49B, or the common wire and the thermal conductor 4101 or the coolantpipe 702 may be connected by using the external wire as shown in FIGS.50A and 50B.

It is to be noted that the case where the coolant pipe 702 which isformed from a material having conductivity is arranged on the backsurface side of the LED backlight is described above; however, even inthe case where the coolant pipe 702 is arranged on the front surfaceside of the LED backlight or even in the case where the coolant pipe 702is arranged on both of the front surface side and the back surface sideof the LED backlight, the coolant pipe can be utilized similarly as theelectrode for applying voltage to the LED in addition to the thermalconductor.

In addition, the thermal conductor 4101 is attached to the backboard 203of the LED backlight 102 in this embodiment mode; however, the thermalconductor 4101 itself may be utilized as a substitute for the backboard203. That is, the LED arrays 205 a to 205 c may be directly attached tothe thermal conductor and utilized. FIGS. 51A and 51B show aconfigurational example of the LED backlight 102 and the cooling device103 in this case.

FIG. 51A shows a plan view of the LED backlight 102 and the coolingdevice 103 shown in FIG. 41 when it is seen from the X-axis side in FIG.41. In addition, FIG. 51B shows a plan view of the LED backlight and thecooling device 103 shown in FIG. 41 when they are seen from the Y-axisside in FIG. 41.

Note that in the cooling device 103, an arrangement of the coolant pipe702 is similar to the arrangement of the cooling device 103 shown inFIG. 45.

In the configurational example of the LED backlight 102 shown in FIGS.51A and 51B, the LED array 205 is directly attached to the thermalconductor 4101 by using the screw 204. Thus, the thermal conductor 4101can be utilized as a substitute for the backboard 203.

By utilizing the thermal conductor 4101 as the substitute for thebackboard 203 in this manner, the LED 201 can be more directly cooledthan the case where the backboard 203 is separately provided when theLED backlight 102 is cooled by using the cooling device, and thus, theLED 201 can be cooled in a shorter time. Accordingly, the coolingefficiency of the LED backlight 102 can be more improved.

In addition, by utilizing the thermal conductor 4101 as the substitutefor the backboard 203 and employing the above-described method, thethermal conductor 4101 can also be utilized as the electrode forapplying voltage to the LED 201. Further, the thermal conductor 4101 canalso be utilized as a shield for electrostatic shielding of the LEDbacklight 102.

In addition, by using a material having high light reflectivity as thethermal conductor 4101, the thermal conductor 4101 can be utilized asthe reflector of the LED 201. Thus, the light emitted from the LED 201is reflected on the thermal conductor 4101 and enters the liquid crystalpanel 101, and thus, the light use efficiency of the LED 201 can beimproved. Further, in the case of arranging three colors of LEDs of R,G, and B alternately, the light of three colors of R, G, and B moreeasily mix with each other since the light is reflected on the thermalconductor 4101. Therefore, uniform white light can enter the liquidcrystal panel 101. Accordingly, the color unevenness can be reduced.

By arranging the thermal conductor between the LED backlight and thecooling device and cooling the LED backlight by the cooling devicethrough the thermal conductor 4101 as in this embodiment mode, the LEDbacklight can be cooled in a shorter time and more efficiently. Inaddition, the thermal conductor can be utilized as the electrode forapplying voltage to the LED, so that the heat generated from the LEDbacklight can be suppressed and the power consumption of the LEDbacklight can also be reduced. Further, the thermal conductor can alsobe utilized as the shield for electrostatic shielding, and thus, theinfluence of the electromagnetic wave or the like on the LED backlight102 is eliminated so that the malfunction or the like of the LEDbacklight can be prevented. Moreover, since the thermal conductor can beutilized as the reflector of the LED 201, the light use efficiency ofthe LED can be improved. In addition, since a particular device or wirefor realizing each of these advantageous effects is not needed to beadditionally provided, the number of the components can be reduced.

Note that various contents described in this embodiment mode may befreely combined and implemented. In addition, the contents described inthis embodiment mode may be freely combined with the contents describedin Embodiment Modes 1 to 4 and implemented.

Embodiment Mode 6

A display device using the LED backlight and the cooling device of theinvention can be applied to various electronic devices. In thisembodiment mode, electronic devices which use a display device using theLED backlight and the cooling device of the invention are given asexamples, and the specific configurational examples thereof aredescribed.

FIGS. 52A and 52B show a configurational example of a display device fora personal computer as an example of electronic devices in thisembodiment mode. FIG. 52A shows a front view of the display device forthe personal computer in this embodiment mode, and FIG. 52B shows a backview of the display device for the personal computer in this embodimentmode.

The display device for the personal computer in this embodiment modeincludes housings 5201 a and 5201 b, a display portion 5202, a support5203, a power supply switch 5204, a cable connecting portion 5205, thecoolant pipe 702, the coolant circulation pump 703, the coolant tank704, and the like.

The display portion 5202, the support 5203, the cable connecting portion5205, the coolant pipe 702, and the like are mainly incorporated in thehousing 5201 a. In addition, the power supply switch 5204 and the likeare mainly incorporated in the housing 5201 b.

The coolant circulation pump 703 and the coolant tank 704 are arrangedon outer sides of the housing 5201 a and 5201 b. For example, thecoolant circulation pump 703 and the coolant tank 704 are arranged overthe support 5203 in FIGS. 52A and 52B. Note that the coolant circulationpump 703 and the coolant tank 704 may be arranged on a back surface sideof the support 5203.

By arranging the coolant circulation pump 703 and the coolant tank 704on the outer sides of the housing 5201 a and 5201 b in this manner,replacement and supplement of the coolant can be easily conducted. Inaddition, since the coolant tank 704 is exposed to the air, heatradiation from the coolant is efficiently conducted. Further, sincespace for arranging the coolant circulation pump 703 and the coolanttank 704 is not necessary to be provided on an inner side of the housing5201 a, the thickness of the display device for the personal computercan be made thinner.

Note that the coolant circulation pump 703 and the coolant tank 704 maybe arranged on inner sides of the housing 5201 a and 5201 b. Inparticular, by arranging the coolant tank 704 on the inner side of thehousing 5201 a, space for arranging the coolant tank 704 is notnecessary to be specially provided on an outer side of the housing 5201a, and thus, useless space can be omitted. In addition, center ofgravity of the display device for the personal computer is lowered, andthus, stability is improved.

A vent 5206 is provided on a back surface side of the housing 5201 a.Thus, heat generated in an inside of the housing such as LED backlightcan be efficiently radiated to an outside of the housing.

In addition, an opening 5207 for leading the coolant pipe 702 isprovided on the back surface side of the housing 5201 a. Then, thecoolant pipe 702 is arranged in the inside of the housing by leading theopening 5207.

Next, FIG. 53 shows a cross-sectional view of the display device for thepersonal computer shown in FIGS. 52A and 52B. Note that FIG. 53 shows across-sectional view of the display device for the personal computershown in FIGS. 52A and 52B when it is seen from an X-axis side in FIGS.52A and 52B.

Note also that FIG. 53 shows a cross-sectional view of the displaydevice for the personal computer in the case of using theconfigurational examples shown in Embodiment Mode 1 as the LED backlightand the cooling device.

The inner side of the housing 5201 a of the display device for thepersonal computer shown in FIG. 53 includes the liquid crystal panel 101having the display portion 5202, the LED backlight 102, the coolant pipe702, a driver circuit board 5301, an optical sheet portion 5303, and thelike. In addition, as an arrangement of these components, the liquidcrystal panel 101, the optical sheet portion 5303, the LED backlight102, the coolant pipe 702, and the driver circuit board 5301 aresequentially arranged toward from a display surface to the back surfaceside.

The liquid crystal panel 101, the optical sheet portion 5303, the LEDbacklight 102, and the driver circuit board 5301 are arranged by beingincorporated in the inner side of the housing 5201 a.

Note that the driver circuit board 5301corresponds to a substrate wherethe power supply or the controller which is necessary for driving theliquid crystal panel 101, the driver circuit for driving the LEDbacklight 102, and the like are arranged.

In addition, the optical sheet portion 5303 corresponds to a portionformed by stacking a plurality of optical functioning sheets of apolarizing film, a phase difference film, a prism sheet, a diffusionfilm, or the like, for example. The optical sheet portion 5303 isarranged between the liquid crystal panel 101 and the LED backlight 102,and the optical sheet portion 5303 has functions of making a wideviewing angle, preventing coloration, and the like by extracting onlylight having a particular polarization direction from light emitted fromthe LED backlight 102, diffusing the light emitted from the LEDbacklight 102, compensating a phase difference of the light emitted fromthe LED backlight 102, and the like.

Here, FIG. 62 shows a cross-sectional view of the display device, inwhich the optical sheet portion 5303 and the periphery thereof areenlarged. The display device shown in FIG. 62 includes the liquidcrystal panel 101, the LED backlight 102, first and second polarizingfilms 6201 and 6204, first and second phase difference films 6202 and6203, a prism sheet 6205, a diffusion film 6206, and the like. Inaddition, as an arrangement of these components, the first polarizingfilm 6201, the first phase difference film 6202, the liquid crystalpanel 101, the second phase difference film 6203, the second polarizingfilm 6204, the prism sheet 6205, the diffusion film 6206, and the LEDbacklight 102 are sequentially arranged toward from the display surfaceto the back surface side. Note that the second phase difference film6203, the second polarizing film 6204, the prism sheet 6205, and thediffusion film 6206 correspond to the optical sheet portion 5303.

Note that the first and second phase difference films 6202 and 6203, andthe prism sheet 6205 are not required to be arranged.

Note that the optical functioning sheets for forming the optical sheetportion 5303 are not limited to the aforementioned examples. Forexample, a luminance improvement film for improving luminance or thelike may be included.

Note that by arranging the driver circuit board 5301 on the back surfaceside of the coolant pipe 702, the light emitted from the LED backlightcan enter the liquid crystal panel 101 without being shielded. Inaddition, the driver circuit board 5301 can also be cooled as well asthe LED backlight 102 can be efficiently cooled by using the coolantpipe 702, and thus, heat generated from the driver circuit board 5301can be suppressed.

Note that there is a case where dew condensation is generated on thesurface of the coolant pipe 702 at the time of cooling the LED backlight102. Then, in order to absorb drop of water generated on the surface ofthe coolant pipe 702, an absorbent material 5302 may be arranged belowor near the coolant pipe 702 as shown in FIG. 53. Thus, the LEDbacklight 102, the driver circuit board 5301, or the like can beprevented from being broken down by drop of water generated on thesurface of the coolant pipe 702.

Note that as the LED backlight and the cooling device, for example, theconfiguration shown in Embodiment Mode 3 or Embodiment Mode 5 may beemployed. Here, FIGS. 54 and 55 show cross-sectional views of thedisplay device for the personal computer in the case of using theconfigurational examples shown in Embodiment Mode 3 or Embodiment Mode 5as the LED backlight and the cooling device.

FIG. 54 shows a cross-sectional view of the display device for thepersonal computer in the case of using the configurational examplesshown in Embodiment Mode 3 as the LED backlight and the cooling device.

The inner side of the housing 5201 a of the display device for thepersonal computer shown in FIG. 54 includes the liquid crystal panel 101for forming the display portion 5202, the LED backlight 102, the coolantpipe 702, a driver circuit board 5301, an optical sheet portion 5303,and the like, similarly to FIG. 53. In addition, as an arrangement ofthese components, the liquid crystal panel 101, the optical sheetportion 5303, the LED backlight 102, and the driver circuit board 5301are sequentially arranged from the display surface toward the backsurface side. The coolant pipe 702 is arranged on the front surface sideof the LED backlight 102 (between the LED arrays which are adjacent toeach other), which is different from the display device for the personalcomputer shown in FIG. 53.

Note that there is a case where dew condensation is generated on thesurface of the coolant pipe 702 at the time of cooling the LED backlight102. Then, in order to absorb drop of water generated on the surface ofthe coolant pipe 702, an absorbent material 5302 may be arranged belowor near the coolant pipe 702. Thus, the LED backlight 102, the drivercircuit board 5301, or the like can be prevented from being broken downby drop of water generated on the surface of the coolant pipe 702.

In addition, by applying a material having high water repellency to theLED backlight 102, waterproofing may be performed. Thus, the LEDbacklight 102 can be prevented from being broken down by attaching dropof water generated on the surface of the coolant pipe 702 to the LEDbacklight 102, in particular, the terminals of the LEDs or the wiringboard.

Next, FIG. 55 shows a cross-sectional view of the display device for thepersonal computer in the case of using the configurational examplesshown in Embodiment Mode 5 as the LED backlight and the cooling device.

The inner side of the housing 5201 a of the display device for thepersonal computer shown in FIG. 55 includes the liquid crystal panel 101for forming the display portion 5202, the LED backlight 102, the coolantpipe 702, a driver circuit board 5301, an optical sheet portion 5303,the thermal conductor 4101, and the like. In addition, as an arrangementof these components, the liquid crystal panel 101, the optical sheetportion 5303, the LED backlight 102, the thermal conductor 4101, thecoolant pipe 702, and the driver circuit board 5301 are sequentiallyarranged toward from the display surface to the back surface side.

The liquid crystal panel 101, the optical sheet portion 5303, the LEDbacklight 102, the thermal conductor 4101, and the driver circuit board5301 are arranged by being incorporated in the inner side of the housing5201 a.

Note that in the case where the thermal conductor 4101 is utilized asthe electrode for applying voltage to the terminal of the LED,electrostatic shielding of the liquid crystal panel 101 and the LEDbacklight 102 can be conducted by not only attaching the thermalconductor 4101 on the back surface side of the LED backlight 102, butalso arranging the thermal conductor 4101 in the inner side of thehousing 5201 a. Thus, influence of electromagnetic wave or the like onthe liquid crystal panel 101 and the LED backlight 102 is removed, sothat a malfunction or the like of the liquid crystal panel 101 and theLED backlight 102 can be prevented.

Note that in FIG. 55, when the thermal conductor 4101 is arranged in theinner side of the housing 5201 a, the thermal conductor 4101 is arrangedonly on the front surface side of the LED backlight 102; however, theinvention is not limited to this. The thermal conductor 4101 may bearranged in the inner side of the housing 5201 a also on the backsurface side of the LED backlight 102. Thus, since electrostaticshielding of the driver circuit board 5301 can also be conducted,influence of electromagnetic wave or the like on the driver circuitboard 5301 is removed, so that a malfunction or the like of the drivercircuit board 5301 can also be prevented.

Note that there is a case where dew condensation is generated on thesurface of the coolant pipe 702 at the time of cooling the LED backlight102. Then, in order to absorb drop of water generated on the surface ofthe coolant pipe 702, an absorbent material 5302 may be arranged belowor near the coolant pipe 702. Thus, the LED backlight 102, the drivercircuit board 5301, or the like can be prevented from being broken downby drop of water generated on the surface of the coolant pipe 702.

FIGS. 56A to 56C show a configurational example of a television as anexample of the electronic devices in this embodiment mode. FIG. 56Ashows a front view of the television in this embodiment mode and FIGS.56B and 56C show rear views of the television in this embodiment mode.

The television in this embodiment mode includes housings 5601 a and 5601b, a display portion 5602, speakers 5603 a and 5603 b, a power supplyswitch 5604, a video input terminal 5605, a cable connecting portion5607, and the like.

The display portion 5602, the speakers 5603 a and 5603 b, the cableconnecting portion 5607, and the like are mainly incorporated in thehousing 5601 a. In addition, the power supply switch 5604, the videoinput terminal 5605, and the like are mainly incorporated in the housing5601 b.

A vent 5606 a is provided on a back surface side of the housing 5601 a.By the vent 5606 a, heat generated in an inside of the housing such asLED backlight can be efficiently radiated to an outside of the housing.

In FIGS. 56A to 56C, the coolant circulation pump 703 and the coolanttank 704 are arranged on an inner side of the housing 5601 a. Note thata coolant tank cover 5608 is provided on a back surface side of thehousing 5601 a, and the coolant tank cover 5608 is usually closed andused (refer to FIG. 56B). In addition, in the case of supplying andreplacing the coolant to the coolant tank 704, the coolant tank cover5608 is usually opened and used (refer to FIG. 56C).

By arranging the coolant circulation pump 703 and the coolant tank 704on the inner side of the housing 5601 a in this manner, the space forarranging the coolant tank 704 is not needed to be specially provided onan outer side of the housing 5601 a, and thus, useless space can beomitted. In addition, center of gravity of the television is lowered,and thus, stability is improved.

Note that a vent 5606 b is arranged in the coolant tank cover 5608.Thus, the heat radiation from the coolant can be efficiently conducted.

Next, FIG. 57 shows a cross-sectional view of the television shown inFIGS. 56A to 56C. Note that FIG. 57 shows a cross-sectional view of thetelevision shown in FIGS. 56A to 56C when it is seen from an X-axis sidein FIGS. 56A to 56C.

Note that FIG. 57 shows a cross-sectional view of the television in thecase of using the configurational examples shown in Embodiment Mode 1 asthe LED backlight and the cooling device.

The inner side of the housing 5601 a of the television shown in FIG. 57includes the liquid crystal panel 101 having the display portion 5602,the LED backlight 102, the coolant pipe 702, a driver circuit board5701, an optical sheet portion 5703, and the like, similarly to FIGS. 53to 55. In addition, as an arrangement of these components, the liquidcrystal panel 101, the optical sheet portion 5703, the LED backlight102, the coolant pipe 702, and the driver circuit board 5701 aresequentially arranged from a display surface toward the back surfaceside.

The liquid crystal panel 101, the optical sheet portion 5703, the LEDbacklight 102, and the driver circuit board 5701 are arranged by beingincorporated in the inner side of the housing 5601 a.

The coolant pump 703 and the coolant tank 704 are arranged on thebackmost surface side of an inside of the housing 5601 a. In FIG. 57,the coolant pump 703 and the coolant tank 704 are arranged in spacewhich is below or near a place in which the driver circuit board 5701 isarranged.

Note that by arranging the driver circuit board 5701 on the back surfaceside of the coolant pipe 702, the light emitted from the LED backlightcan enter the liquid crystal panel 101 without being shielded. Inaddition, the driver circuit board 5701 can be cooled as well as the LEDbacklight 102 can be efficiently cooled by using the coolant pipe 702,and thus, heat generated from the driver circuit board 5701 can besuppressed.

Note that there is a case where dew condensation is generated on thesurface of the coolant pipe 702 at the time of cooling the LED backlight102. Then, in order to absorb drop of water generated on the surface ofthe coolant pipe 702, an absorbent material 5702 may be arranged belowor near the coolant pipe 702. Thus, the LED backlight 102, the drivercircuit board 5701, or the like can be prevented from being broken downby drop of water generated on the surface of the coolant pipe 702.

In addition, similarly to the televisions shown in FIGS. 54 and 55, theconfigurations shown in Embodiment Mode 3 or Embodiment Mode 5 may beemployed as the LED backlight and the cooling device, for example. Here,FIGS. 58 and 59 show cross-sectional views of the television in the caseof using the configurational example shown in Embodiment Mode 3 orEmbodiment Mode 5 as the LED backlight and the cooling device.

FIG. 58 shows a cross-sectional view of the television in the case ofusing the configurational examples shown in Embodiment Mode 3 as the LEDbacklight and the cooling device. The coolant pipe 702 is arranged onthe front surface side of the LED backlight 102 (between the LED arrayswhich are adjacent to each other), which is different from thetelevision shown in FIG. 57.

FIG. 59 shows a cross-sectional view of the television in the case ofusing the configurational examples shown in Embodiment Mode 5 as the LEDbacklight and the cooling device. The thermal conductor 4101 is arrangedbetween the LED backlight 102 and the coolant pipe 702, which isdifferent from the television shown in FIG. 57.

By applying the display device using the LED backlight and the coolingdevice of the invention in this manner, a clear image with reduceddisplay unevenness or color evenness can be viewed.

Note that each of the display device and the electronic device in thisembodiment mode may have a function of displaying information on theamount or a water level of the coolant stored in the coolant tank, inthe display portion. Further, the display device and the electronicdevice in this embodiment mode may have a function of displaying cautionfor promoting the supplement of the coolant in the display portion, inthe case where the amount becomes smaller than a reference value or thewater level of the coolant stored in the coolant tank becomes lower thana reference value.

For example, by employing a method described below, information on theamount or a water level of the coolant stored in the coolant tank, thecaution for promoting the supplement of the coolant, or the like can bedisplayed in the display portion. This method is described withreference to FIG. 60.

For example, a sensor 6001 is arranged in the coolant tank 704. Thesensor 6001 detects the water level of the coolant 701 and outputs asignal based on the water level of the coolant. The signal output fromthe sensor 6001 is input into a controller 6003 arranged in a drivercircuit board 6002. The controller 6003 generates a signal fordisplaying the water level of the coolant. In addition, in the casewhere the water level of the coolant stored in the coolant tank becomeslower than a reference value, a signal for displaying the caution forpromoting the supplement of the coolant is generated. Then, a signal fordisplaying caution of the water level of the coolant and for promotingthe supplement of the coolant is input into the liquid crystal panel 101having the display portion. Thus, the caution of the water level of thecoolant and for promoting the supplement of the coolant can be displayedin the display portions.

By displaying information on the amount or the water level of thecoolant stored in the coolant tank, the caution for promoting thesupplement of the coolant, or the like in the display portion in thismanner, shortage of the coolant can be prevented beforehand, and thus,decrease of the cooling efficiency of the LED backlight caused by theshortage of the coolant can be prevented.

Note that with respect to a driving method of the. LED backlight, adriving method where the LEDs are continuously turned on during oneframe period displaying an image for one scene of pictures may beperformed, or a driving method where some or all of the LEDs for formingthe LED backlight are turned off every time an image is switched may beperformed.

For example, by turning off the all of the LEDs forming the LEDbacklight every time the images are switched, a black image on theentire screen can be inserted between an image displayed at present andan image displayed next. Alternatively, by sequentially turning off someof the LEDs forming the LED backlight every time the images areswitched, a black image on a part of the screen can be inserted betweenan image displayed at present and an image displayed next.

By turning off some or the all of the LEDs fainting the LED backlightevery time the images are switched in this manner, a blur of a movingimage caused by an after image which is perceived by retinas of a personcan be improved, and thus, a moving image having excellent image qualitycan be displayed.

In addition, as the driving method of the LED backlight, fieldsequential driving where three colors of LEDs of R, and B aretime-divided to be sequentially turned on in one frame period may beperformed. By performing the field sequential driving, the light ofthree colors of R, G, and B easily mix with each other so that ahigh-definition image having high color reproductivity can be displayed.

Note that the configurational examples of the electronic devices shownin this embodiment mode are only just examples, and thus, the inventionis not limited to the contents described in this embodiment mode.

Note that the contents described in this embodiment mode may be freelycombined with the contents described in Embodiment Modes 1 to 5 andimplemented.

Embodiment Mode 7

In addition to the examples illustrated in Embodiment Mode 6, anavigation system, an audio reproducing device (e.g., a car audio oraudio component set), a computer such as a laptop computer, a gamemachine, an image reproducing device arranged with a recording medium(specifically, a device for reproducing a content of a recording mediumsuch as a digital versatile disc (DVD) and having a display fordisplaying an reproduced image), and the like are given as electronicdevices which apply a display device using the LED backlight and thecooling device of the invention. FIGS. 61A to 61D show specific examplesof the electronic devices.

FIG. 61A shows a display device for displaying information, whichincludes a housing 6101, a support medium 6102, a display portion 6103,a speaker portion 6104, a video input terminal 6105, and the like. Theinvention can be applied to a display device for forming the displayportion 6103, and the clear image where the display unevenness or thecolor evenness is reduced can be viewed by employing the invention. Notethat the display device for displaying information includes all ofdisplay devices for displaying information such as those for personalcomputers, television broadcast reception, and advertisement display.

In particular, by applying the LED backlight and the cooling device ofthe invention to a display device for displaying information used fordigital television broadcast reception, an advantageous effect ofdecrease in the display unevenness or the color unevenness becomesgreater so that clearer images can be viewed.

FIG. 61B shows a laptop computer, which includes a main body 6106, ahousing 6107, a display portion 6108, a keyboard 6109, an externalconnecting port 6110, a pointing device 6111, and the like. Theinvention can be applied to a display device for forming the displayportion 6108, and the clear image where the display unevenness or thecolor evenness is reduced can be viewed by employing the invention.

FIG. 61C shows a portable image reproducing device provided with arecording medium (specifically, a DVD player), which includes a mainbody 6112, a housing 6113, display portions A6114 and B36115, arecording medium (e.g., DVD) reading portion 6116, operating keys 6117,a speaker portion 6118, and the like. The display portion A6114 mainlydisplays image data and the display portion B6115 mainly displaystextual data. The invention can be applied to a display device forforming the display portions A6114 and B6115 and the clear image wherethe display unevenness or the color evenness is reduced can be viewed byemploying the invention. Note that the image reproducing device providedwith the recording medium includes a home-use game machine and the like.

The LED backlight and the cooling device of the, invention can beutilized not only as a backlight of a liquid crystal panel but also as alighting device arranged with a cooling device. For example, FIG. 61Dshows a projector, which includes a housing 6119, a lens 6120, operatingbuttons 6121, a light-emitting portion 6122, and the like. The inventioncan be applied to a lighting device forming the light-emitting portion6122 which is incorporated inside of a projector. A high quality imagewhere the display unevenness or the color evenness is reduced can beviewed by employing the invention.

In addition, in the case of utilizing the LED backlight and the coolingdevice of the invention as the lighting device, the liquid crystal panelis not necessary to be arranged. The LED backlight and the coolingdevice of the invention may be utilized as a lighting device such asroom light, a lighting device for an inside of a car, or a displayboard.

Further, the cooling device of the invention may be utilized not only asthe cooling device for cooling the LED backlight, but also as thecooling device of the display device. For example, it may be utilized asa cooling device of a display device using FED.

As described above, an application range of the invention is extremelywide and the invention can be applied to electronic devices in allfields. In addition, the electronic devices in this embodiment mode mayemploy any one of the configurations described in Embodiments Modes 1 to6.

The present application is based on Japanese Patent application No.2005-379956 filed on Dec. 28, 2005 with the Japanese Patent Office, theentire contents of which are hereby incorporated by reference.

1-25. (canceled)
 26. A display device comprising: a liquid crystalpanel; and a back light adjacent to the liquid crystal panel, whereinthe back light includes a thermal conductor, a plurality of boardsformed over the thermal conductor, a plurality of light-emitting diodesformed over the plurality of boards, and a reflecting portion formedover the thermal conductor.
 27. A display device according to claim 26,further comprising a pipe in which a coolant flows to cool the backlight.
 28. A display device according to claim 26, wherein thereflecting portion covers the plurality of boards.
 29. A display deviceaccording to claim 26, wherein the liquid crystal panel includes a thinfilm transistor which contains InGaZnO as a semiconductor.
 30. A displaydevice according to claim 26, wherein the thermal conductor contains ametal selected from the group consisting of copper, iron, aluminum, anda stainless steel.
 31. A display device according to claim 26, whereinthe display device is incorporated in one selected from the groupconsisting of a television set, a computer, an image reproducing device,and a projector.
 32. A display device comprising: a liquid crystalpanel; and a back light adjacent to the liquid crystal panel, whereinthe back light includes a thermal conductor, a plurality of boardsformed over the thermal conductor, a plurality of light-emitting diodesformed over the plurality of boards, and a reflecting portion containinga plastic formed over the thermal conductor.
 33. A display deviceaccording to claim 32, further comprising a pipe in which a coolantflows to cool the back light.
 34. A display device according to claim32, wherein the reflecting portion covers the plurality of boards.
 35. Adisplay device according to claim 32, wherein the liquid crystal panelincludes a thin film transistor which contains InGaZnO as asemiconductor.
 36. A display device according to claim 32, wherein thethermal conductor contains a metal selected from the group consisting ofcopper, iron, aluminum, and a stainless steel.
 37. A display deviceaccording to claim 32, wherein the display device is incorporated in oneselected from the group consisting of a television set, a computer, animage reproducing device, and a projector.
 38. A display devicecomprising: a liquid crystal panel; a back light adjacent to the liquidcrystal panel, wherein the back light includes a thermal conductor, aplurality of boards formed over the thermal conductor, a plurality oflight-emitting diodes formed over the plurality of boards, and areflecting portion formed over the thermal conductor; and a diffusionfilm, a prism sheet, and a polarizing film interposed between the liquidcrystal panel and the back light.
 39. A display device according toclaim 38, further comprising a pipe in which a coolant flows to cool theback light.
 40. A display device according to claim 38, wherein thereflecting portion covers the plurality of boards.
 41. A display deviceaccording to claim 38, wherein the liquid crystal panel includes a thinfilm transistor which contains InGaZnO as a semiconductor.
 42. A displaydevice according to claim 38, wherein the thermal conductor contains ametal selected from the group consisting of copper, iron, aluminum, anda stainless steel.
 43. A display device according to claim 38, whereinthe display device is incorporated in one selected from the groupconsisting of a television set, a computer, an image reproducing device,and a projector.
 44. A display device comprising: a liquid crystalpanel; and a back light adjacent to the liquid crystal panel, whereinthe back light includes a thermal conductor, a plurality of boardsformed over the thermal conductor, a plurality of light-emitting diodesformed over the plurality of boards, and a reflecting portion containinga plastic formed over the thermal conductor; and a diffusion film, aprism sheet, and a polarizing film interposed between the liquid crystalpanel and the back light.
 45. A display device according to claim 44,further comprising a pipe in which a coolant flows to cool the backlight.
 46. A display device according to claim 44, wherein thereflecting portion covers the plurality of boards.
 47. A display deviceaccording to claim 44, wherein the liquid crystal panel includes a thinfilm transistor which contains InGaZnO as a semiconductor.
 48. A displaydevice according to claim 44, wherein the thermal conductor contains ametal selected from the group consisting of copper, iron, aluminum, anda stainless steel.
 49. A display device according to claim 44, whereinthe display device is incorporated in one selected from the groupconsisting of a television set, a computer, an image reproducing device,and a projector.